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A battery charger is a device used to put energy into a cell or (rechargeable) battery by forcing an electric current through it.

The charge current depends upon the technology and capacity of the battery being charged. For example, the current that should be applied to recharge a 12 V car battery will be very different from the current for a mobile phone battery.

Types of battery chargers

Simple

A simple charger works by connecting a constant DC power source to the battery being charged. The simple charger does not alter its output based on time or the charge on the battery. This simplicity means that a simple charger is inexpensive, but there is a tradeoff in quality. Typically, a simple charger takes longer to charge a battery to prevent severe over-charging. Even so, a battery left in a simple charger for too long will be weakened or destroyed due to over-charging.

Trickle

A trickle charger is a kind of simple charger that charges the battery slowly, at the self-discharge rate. A trickle charger is the slowest kind of battery charger. A battery can be left in a trickle charger indefinitely. Leaving a battery in a trickle charger keeps the battery “topped up” but never over-charges.

Timer-based

The output of a timer charger is terminated after a pre-determined time. Timer chargers were the most common type for high-capacity Ni-Cd cells in the late 1990s for example (low-capacity consumer Ni-Cd cells were typically charged with a simple charger).

Often a timer charger and set of batteries could be bought as a bundle and the charger time was set to suit those batteries. If batteries of lower capacity were charged then they would be overcharged, and if batteries of higher capacity were charged they would be only partly charged. With the trend for battery technology to increase capacity year on year, an old timer charger would only partly charge the newer batteries.

Timer based chargers also had the drawback that charging batteries that were not fully discharged, even if those batteries were of the correct capacity for the particular timed charger, would result in over-charging.

Intelligent

Output current depends upon the battery’s state. An intelligent charger may monitor the battery’s voltage, temperature and/or time under charge to determine the optimum charge current at that instant. Charging is terminated when a combination of the voltage, temperature and/or time indicates that the battery is fully charged.

For Ni-Cd and NiMH batteries, the voltage across the battery increases slowly during the charging process, until the battery is fully charged. After that, the voltage decreases, which indicates to an intelligent charger that the battery is fully charged. Such chargers are often labeled as a ΔV, or “delta-V,” charger, indicating that they monitor the voltage change.

A typical intelligent charger fast-charges a battery up to about 85% of its maximum capacity in less than an hour, then switches to trickle charging, which takes several hours to top off the battery to its full capacity.

Fast

Fast chargers make use of control circuitry in the batteries being charged to rapidly charge the batteries without damaging the cells’ elements. Most such chargers have a cooling fan to help keep the temperature of the cells under control. Most are also capable of acting as a standard overnight charger if used with standard NiMH cells that do not have the special control circuitry. Some fast chargers, such as those made by Energizer, can fast-charge any NiMH battery even if it does not have the control circuit.

Pulse

Some chargers use pulse technology in which a pulse is fed to the battery. This DC pulse has a strictly controlled rise time, shape, pulse width, pulse repetition rate (frequency) and amplitude. This technology is said to work with any size, voltage, capacity or chemistry of batteries, including automotive and valve-regulated batteries.

Several kinds of pulse charging are patented  .

Some chargers use pulses to check the current battery state when the charger is first connected, then use constant current charging during fast charging, then use pulse charging as a kind of trickle charging to maintain the charge.

Some chargers use “negative pulse charging”, also called “reflex charging” or “burp charging”. Such chargers use both positive and brief negative current pulses. Such chargers don’t work any better than pulse chargers that only use positive pulses .

Inductive

Inductive battery chargers use electromagnetic induction to charge batteries. A charging station sends electromagnetic energy through inductive coupling to an electrical device, which stores the energy in the batteries. This is achieved without the need for metal contacts between the charger and the battery. It is commonly used in electric toothbrushes, and other devices used in bathrooms, because there is no risk of electrocution.

USB-based

Since the Universal Serial Bus specification provides for a five-volt power supply, it’s possible to use a USB cable as a power source for recharging batteries. Products based on this approach include chargers designed to charge standard NiMH cells, and custom NiMH batteries with built-in USB plugs and circuitry which eliminate the need for a separate charger. Moixa Energy patented a design of batteries, branded USBCELL, that incorporate their own USB chargers internally, complete with their own plugs. In the currently available AA battery design, the positive end of the battery doubles as a flip-cap for the built-in USB plug.

Charge rate

This is often denoted as C and signifies a charge or discharge rate equal to the capacity of a battery divided by 1 hour. For example C for a 1600 mAh battery would be 1600 mA (or 1.6 amps). 2C is twice this rate and 1/2C is half the rate.

Applications

Since a battery charger is intended to be connected to a battery, it may not have voltage regulation or filtering of the DC voltage output. Battery chargers equipped with both voltage regulation and filtering may be identified as battery eliminators.

Mobile phone charger

Most mobile phone chargers are not really chargers, only adapters that provide a power source for the charging circuitry which is almost always contained within the mobile phone. Mobile phones can usually accept relatively wide range of voltages, as long as it is sufficiently above the phone battery’s voltage. However, if the voltage is too high, it can damage the phone. Mostly, the voltage is 5 volts or slightly higher, but it can sometimes vary up to 12 volts when the power source is not loaded.

Battery chargers for mobile phones and other devices are notable in that they come in a wide variety of DC connector-styles and voltages, most of which are not compatible with other manufactuers’ phones or even different models of phones from a single manufacturer.

Users of publicly accessible charging kiosks must be able to cross-reference connectors with device brands/models and individual charge parameters and thus ensure delivery of the correct charge for their mobile device. A database-driven system is one solution, and is being incorporated into some of the latest designs of charging kiosks.

There are also human-powered chargers sold on the market, which typically consists of a dynamo powered by a hand crank and extension cords. There are also solar chargers.

China and other countries are making a national standard on mobile phone chargers using the USB standard.

Battery charger for vehicles

There are two main types of charges for vehicles:

• To recharge a fuel vehicle’s starter battery, where a modular charger is used.
• To recharge an electric vehicle (EV) battery pack.

Battery electric vehicle

These vehicles include a battery pack, so generally use series charger.

A 10 Ampere-hour battery could take 15 hours to get fully charged from a fully discharged condition with a 1 Ampere charger as it would require roughly 1.5 times the battery’s capacity.

Public EV charging heads (aka: stations) provide 6kW (host power of 208 to 240 VAC off a 40 amp circuit). 6kW will recharge an EV 6 times faster than 1kW overnight charging.

Rapid charging gives even faster recharge times and are only limited by available AC power and the type of charging system.

On board EV chargers (change AC power to DC power to recharge the EV’s pack) can be:

• Isolated: they make no connection between the A/C electrical mains and the batteries being charged. Isolated chargers can be put in parallel using more than one power source to boost charge current and reduce recharging time.

• Non-isolated: the battery pack has a connection the A/C outlet’s wiring. Un-isolated chargers can not be using in parallel, and should be disconnected from each other even with the AC power off.

Power Factor Correction (PFC) chargers can more closely approach the maximum current the plug can deliver, shortening charging time.

Some battery electric vehicle charging devices includes:

• Manzanita Micro Power factor correction (PFC) PFC series chargers (mid price range) (non-isolated) (90 to 240 VAC input, 12 to 366 VDC output).
• Russco  SC and DSO series chargers (low price range) (non-isolated) (120 VAC input, 72 to 120 VDC battery packs, 120 to 156 VDC pack require their AC input boost transformer).
• Zivan NG series chargers (mid price range) (isolated).
• BRUSA Elektronik AG (high price range) (isolated).

Charge stations

There is a list of public EV charging stations in the U.S.A.^]

Project Better Place is deploying a network of charge stations. It also subsidize vehicle battery costs through leases and credits.

Prolonging battery life

Many rumors circulate about the best practices to prolong battery life. What practices are best depend on the type of battery. It is rumored that Nickel-based cells, such as NiMH and NiCd, need to be fully discharged before each charge, or else the battery loses capacity over time in a phenomenon known as memory effect. However, this is only partially accurate: nickel alloy cells can be charged at any point throughout their discharge cycle–they do not have to be fully discharged. Memory effect should instead be prevented by fully discharging the battery once a month (once every 30 charges). This extends the life of the battery since memory effect is prevented while avoiding full charge cycles which are known to be hard on all types of dry-cell batteries, eventually resulting in a permanent decrease in battery capacity.

Most modern cell phones, laptops, and most electric vehicles use Lithium-ion batteries. Contrary to some recommendations, these batteries actually last longest if the battery is not fully charged; fully charging and discharging them will degrade their capacity relatively quickly. Degradation occurs faster at higher temperatures. Lithium batteries degrade more while fully charged than if it is only 40% charged. The conditions of high temperature combined with full charge are exactly the scenario occurring when a laptop computer is run on AC power. Degradation in lithium-ion batteries is caused by an increased internal battery resistance due to cell oxidation. This decreases the efficiency of the battery, resulting in less net current available to be drawn from the battery.

Internal combustion engine vehicles, such as boats, RVs, ATVs, motorcycles, cars, trucks, and more use lead acid batteries. These batteries employ a sulfuric acid electrolyte and can generally be charged and discharged without exhibiting memory effect, though sulfation (a chemical reaction in the battery which deposits a layer of sulfates on the lead) will occur over time. Keeping the electrolyte level in the recommended range is necessary. When discharged, these batteries should be recharged immediately in order to prevent sulfation. These sulfates are electrically insulating and therefore interfere with the transfer of charge from the sulfuric acid to the lead, resulting in a lower maximum current than can be drawn from the battery. Sulfated lead acid batteries typically need replacing. Good ventilation and avoidance of ignition sources (e.g., sparks) is wise when recharging, since charging a lead acid battery generates highly explosive hydrogen gas.

This article is come from http://en.wikipedia.org/wiki/Battery_charger

Looking for the perfect notebook PC to suit your needs? With LAPTOP’s Laptop Buying Guide, we’ve made selecting the best machine for your needs easy. Here you’ll find tips, advice, and all the information you need to make the smartest buying decision.

What Are Budget Notebooks?
As the name implies, budget notebooks are models aimed at price-conscious buyers who need a basic computer at an affordable price. For our definition, we look for a price of $999 or less, but you can find very good deals in the $799 to $899 range.

What Are All-Purpose Notebooks?
All-purpose notebooks represent the sweet spot for the industry. This category comprises thin-and-light models with 13.3-inch or 14-inch screens, as well as the typical mainstream portable with a screen up to 15.4 inches in size.

What Are Business Notebooks?
Business notebooks are thin-and-light or mainstream models that include the security, connectivity, and durability features a professional user would need. Notebooks intended for corporate use have all that, plus manageability features and a stable platform so the OS image of units deployed now will match that of machines ordered six to nine months from now.

What Are Ultraportable Notebooks?
Thinner and lighter than even a thin-and-light notebook, an ultraportable notebook is a machine that weighs less than 4 pounds but still delivers the functionality of a full PC. Screens are smaller, keyboards are tighter, and processors are generally less powerful than with a full-size notebook.

What Are Desktop Replacement Notebooks?
A desktop replacement is a notebook with a 17-inch screen or larger. While panels that size in a portable were unthinkable a few years ago, they are now commonplace-and some laptops have 19- and even 20-inch LCDs. With such a screen as the centerpiece, most desktop replacement machines focus on the video, multimedia, and gaming experience.

What Are Gaming Notebooks?
A gaming notebook puts 3D graphics performance above all else. That means a powerful GPU (or two) and top-of-the-line CPU, of course, but also fast memory and hard-drive subsystems. A large LCD with fast response times and good grayscale performance (to better render shadow detail) is also a must, and a good audio system doesn’t hurt.

What Are Tablet PCs?
Tablet PCs are arguably the most versatile machines in the laptop genus. Their screens react to input from a finger or stylus, letting you enter notes and drawings freehand. Light weight and long battery life make them suitable for life on the go.

What Are Rugged Notebooks?
Rugged notebooks are machines that have extra protection against a range of environmental and situational hazards. They are designed to work in harsh conditions: dusty construction sites and factories; outdoors in the heat, cold, and wet; and in moving vehicles where they are subjected to shock and vibration.

Who Are Student Notebooks For?
Student notebooks are designed with high-school and college attendees in mind. They can be used for both schoolwork and play (more of the latter, we suspect), so they need decent power and components good enough to let them act as music library, stereo system, DVD player, and YouTube-creation stations.

More laptop buying guide, please visit http://www.laptopmag.com/buying-guides/laptops/laptop-buying-guide.aspx

Admit it. Come out of denial. You know your laptop that was supercool 2 years ago now gets 15 minutes of battery life. It sucks and we all share the same problem eventually. Laptop batteries (and many others) will start to lose their total charging capacity after awhile. It’s slow so we usually don’t notice it until years later. But when it happens, you can’t help but go insane. Laptop batteries usually cost a fortune (my 12-inch powerbook battery is like $130). This is why you should take the road less traveled and rebuild your battery.

So what do you have to do? Well it’s not too complicated, you just have to basically replace the individual cells inside of the battery casing. Ever have an R/C car and you had to buy those $20 battery packs at Radio Shack for them? Well if you take a close look, it’s usually just 6 batteries saran-wrapped together with a proprietary plug. Same goes for these laptop batteries.

Now before we go any further, let me issue a warning. Although most of us think we’re invincible, we’re not. This is something that could lead to harm if you don’t follow everything directly. If you’re new to hacking apart electronics and what not, don’t proceed. Have a specialist help you. We’re not responsible for anything that may happen, mkay? Kay.

Allright so let’s get started. Take your fork out of the electrical socket for a moment and check it.
Remove your battery from your laptop. Try to get it drained all the way if you can. Look at the label on your battery. Somewhere near the warning where it says ‘Don’t do this, don’t do that’blah blah blah’ you should see a model number for the battery pack. Probably something along the lines of ‘Lithium Ion Battery Pack No. Pry off the cover of your battery pack like so.

….which will reveal something like below.

Individual cells.

If you have a powerbook like me, it’ll look like this:

So. Now we’ve got a bunch of cells. Cute. Find the part number for them. As you can see in the pic above the powerbook battery, the number is printed directly on the wrapping. In this case it’s CGP345010. Ok great. What’s that mean? Google it and see. Ahhh! It’s made by Panasonic. Wonderful. Now we have to go get replacements. If there’s 6 cells, you’ll obviously need 6 new ones. Try this website for ordering them.

Get out your xacto knife, wire cutters, etc. for this. You’ll need to carefully remove all the cells. Each battery pack is different so we can’t say how it’ll work out for you. Just be careful and don’t throw away the old ones.

Take out all the metal contacts etc. until you have yourself a blank battery tray.

Chances are your battery cells will come with wires on there for connecting it to something. No. We don’t want these. We need this to lay in the tray! Remove your black and red wires but keep any others left. It’s usually to keep them from short-circuiting. Next, take any coating and tops off your old batteries and move them carefully onto the new ones. After you’re done, you should have naked old batteries, and new batteries that look like the old ones.

Next, you need to get contact going. Obviously using metal. You can either solder them together properly with a metal strip on the front, or just try positioning the metal correctly inside the case with the cells. I did the 2nd method and it worked for me after some tinkering around.

Almost there. Put everything back together like it was and make sure you check out your finished product with a multimeter to make sure there’s a current. If all is well, throw it all back together and then into your laptop. Charge it up completely without using it and voila. You my friend, are set.

Much thanks to electronics lab, and reader [surfer] for the tips and pics! In my opinion, the PowerBook battery is much easier, but don’t let that stop you! Just take care!

News from http://www.engadget.com/2005/06/28/how-to-rebuild-your-laptop-battery/

Lithium-ion batteries supply the power for cell phones and PDAs, and larger devices such as laptops, cordless screwdrivers and lawnmowers are becoming increasingly dependent on this power source. The advantage of these power storage devices lies in their high energy density and voltage (up to four volts). In terms of safety, however, they have one disadvantage – the organic electrolytes are inflammable and can easily catch fire.

This has already resulted in several fires and subsequent recall campaigns. Researchers at the Fraunhofer Institute for Silicate Research ISC in Würzburg have optimized the safety of these batteries. “We have succeeded in replacing the inflammable organic electrolytes with a non-flammable polymer that retains its shape,” says ISC team leader Dr. Kai-Christian Möller.

“This considerably enhances the safety of lithium-ion batteries. What’s more, because it is a solid substance, the electrolyte cannot leak out of the battery.” The polymer used by the researchers is derived from the Ormocer® group of substances – a compound with silicon-oxygen chains that form an inorganic structure to which organic side chains become attached. The big challenge is to ensure that the polymers will efficiently conduct the lithium ions that supply the power for the cell phone and the PDA. “Normally, the more solid a polymer is, the less conductive it becomes. But we had numerous parameters that we could adjust – for example, we can use coupling elements with two, three or four arms. As a result, we have more possibilities with Ormocer®s than with a single type of plastic,” says Möller.

A prototype of the new lithium-ion batteries already exists, and the researchers will be presenting it at Hannover Messe (Hall 13, Stand E20). However, between three and five years are likely to elapse before the battery will cross shop counters in laptop computers, PDAs and cordless screwdrivers, the expert believes. The conductivity of the polymer needs further improvement to enable the battery to deliver or store as much power as possible in as short a time as possible. Once this happens, though, it is quite realistic to expect this type of battery – in conjunction with a capacitor – to be able to compete with the lead batteries in cars.

Redox flow batteries store solar energy Solar cells can be seen on the roofs of more and more houses today. The energy supplied by the sun and the wind is also increasingly being used on a large scale – in wind turbines and solar parks. But the energy supplied by the sun and the wind does not usually correspond to power requirements: On sunny days the solar cells often deliver more electricity than is needed, while solar energy may be in short supply when the sky is overcast. The amount of energy harvested from wind turbines fluctuates in a similar way.

In private solar energy plants, the surplus energy is stored in lead batteries until it is needed. The drawback of these storage systems is that they can only survive a limited number of cycles and normally have to be replaced after three to five years. In wind and solar parks, the energy is conserved by pumped storage plants. These, too, have a disadvantage: They have a relatively low rate of efficiency, which means that a lot of energy is lost. What is more, they take up a great deal of space. Redox flow batteries offer an alternative to lead batteries and pumped storage plants: They have a comparable energy density, but their service life is nearly ten times as long as that of lead batteries. So far, however, they are quite expensive in relation to their performance and energy density.

Researchers at the Fraunhofer Institute for Chemical Technology ICT in Pfinztal intend to change that situation in the years ahead: “We have developed the prototype of a redox flow battery that enables us to test various electrode materials, membranes and electrolytes as flexibly as possible,” reports ICT group leader Dr. Jens Tübke. “In this way, we can compare different redox systems in the same test set-up. This allows us to work out precisely what are the pros and cons of each system. It is not possible to compare the systems on the basis of existing documentation, as of course everyone measures them in a different test set-up.”

News from http://www.sciencedaily.com/releases/2008/04/080411151001.htm

We often get puzzled by announcements of new batteries that are said to offer very high energy densities, deliver 1000 charge/discharge cycle and are paper-thin. Are they real? Perhaps — but not in one and the same battery. While one battery type may be designed for small size and long runtime, this pack will not last and wear out prematurely. Another battery may be built for long life, but the size is big and bulky. A third battery may provide all the desirable attributes, but the price would be too high for commercial use.

Battery manufacturers are well aware of customer needs and have responded by offering packs that best suit the specific applications. The mobile phone industry is an example of clever adaptation. Emphasis is placed on small size, high energy density and low price. Longevity comes in second.

The inscription of NiMH on a battery pack does not automatically guarantee high energy density. A prismatic Nickel-Metal Hydride battery for a mobile phone, for example, is made for slim geometry. Such a pack provides an energy density of about 60Wh/kg and the cycle count is around 300. In comparison, a cylindrical NiMH offers energy densities of 80Wh/kg and higher. Still, the cycle count of this battery is moderate to low. High durability NiMH batteries, which endure 1000 discharges, are commonly packaged in bulky cylindrical cells. The energy density of these cells is a modest 70Wh/kg.

Compromises also exist on lithium-based batteries. Li‑ion packs are being produced for defense applications that far exceed the energy density of the commercial equivalent. Unfortunately, these super-high capacity Li‑ion batteries are deemed unsafe in the hands of the public and the high price puts them out of reach of the commercial market.

In this article we look at the advantages and limitations of the commercial battery. The so-called miracle battery that merely live in controlled environments is excluded. We scrutinize the batteries not only in terms of energy density but also longevity, load characteristics, maintenance requirements, self-discharge and operational costs. Since NiCd remains a standard against which other batteries are compared, we evaluate alternative chemistries against this classic battery type.

Nickel Cadmium (NiCd) — mature and well understood but relatively low in energy density. The NiCd is used where long life, high discharge rate and economical price are important. Main applications are two-way radios, biomedical equipment, professional video cameras and power tools. The NiCd contains toxic metals and is environmentally unfriendly.

Nickel-Metal Hydride (NiMH) — has a higher energy density compared to the NiCd at the expense of reduced cycle life. NiMH contains no toxic metals. Applications include mobile phones and laptop computers.

Lead Acid — most economical for larger power applications where weight is of little concern. The lead acid battery is the preferred choice for hospital equipment, wheelchairs, emergency lighting and UPS systems.

Lithium Ion (Li‑ion) — fastest growing battery system. Li‑ion is used where high-energy density and lightweight is of prime importance. The technology is fragile and a protection circuit is required to assure safety. Applications include notebook computers and cellular phones.

Lithium Ion Polymer (Li‑ion polymer) — offers the attributes of the Li-ion in ultra-slim geometry and simplified packaging. Main applications are mobile phones.
Figure 1 compares the characteristics of the six most commonly used rechargeable battery systems in terms of energy density, cycle life, exercise requirements and cost. The figures are based on average ratings of commercially available batteries at the time of publication.

	NiCd	NiMH	Lead Acid	Li-ion	Li-ion polymer	Reusable Alkaline
Gravimetric Energy Density (Wh/kg)	45-80	60-120	30-50	110-160	100-130	80 (initial)
Internal Resistance (includes peripheral circuits) in mW	100 to 2001 6V pack	200 to 3001 6V pack	<1001 12V pack	150 to 2501 7.2V pack	200 to 3001 7.2V pack	200 to 20001 6V pack
Cycle Life (to 80% of initial capacity)	15002	300 to 5002,3	200 to 3002	500 to 10003	300 to 500	503 (to 50%)
Fast Charge Time	1h typical	2-4h	8-16h	2-4h	2-4h	2-3h
Overcharge Tolerance	moderate	low	high	very low	low	moderate
Self-discharge / Month (room temperature)	20%4	30%4	5%	10%5	~10%5	0.3%
Cell Voltage (nominal)	1.25V6	1.25V6	2V	3.6V	3.6V	1.5V
Load Current - peak - best result	20C 1C	5C 0.5C or lower	5C7 0.2C	>2C 1C or lower	>2C 1C or lower	0.5C 0.2C or lower
Operating Temperature (discharge only)	-40 to 60°C	-20 to 60°C	-20 to 60°C	-20 to 60°C	0 to 60°C	0 to 65°C
Maintenance Requirement	30 to 60 days	60 to 90 days	3 to 6 months9	not req.	not req.	not req.
Typical Battery Cost (US$, reference only)	$50 (7.2V)	$60 (7.2V)	$25 (6V)	$100 (7.2V)	$100 (7.2V)	$5 (9V)
Cost per Cycle (US$)11	$0.04	$0.12	$0.10	$0.14	$0.29	$0.10-0.50
Commercial use since	1950	1990	1970	1991	1999	1992

Figure 1: Characteristics of commonly used rechargeable batteries

1. Internal resistance of a battery pack varies with cell rating, type of protection circuit and number of cells. Protection circuit of Li‑ion and Li-polymer adds about 100mW.
2. Cycle life is based on battery receiving regular maintenance. Failing to apply periodic full discharge cycles may reduce the cycle life by a factor of three.
3. Cycle life is based on the depth of discharge. Shallow discharges provide more cycles than deep discharges.
4. The discharge is highest immediately after charge, then tapers off. The NiCd capacity decreases 10% in the first 24h, then declines to about 10% every 30 days thereafter. Self-discharge increases with higher temperature.
5. Internal protection circuits typically consume 3% of the stored energy per month.
6. 1.25V is the open cell voltage. 1.2V is the commonly used value. There is no difference between the cells; it is simply a method of rating.
7. Capable of high current pulses.
8. Applies to discharge only; charge temperature range is more confined.
9. Maintenance may be in the form of ‘equalizing’ or ‘topping’ charge.
10. Cost of battery for commercially available portable devices.
11. Derived from the battery price divided by cycle life. Does not include the cost of electricity and chargers.

Observation: It is interesting to note that NiCd has the shortest charge time, delivers the highest load current and offers the lowest overall cost-per-cycle, but has the most demanding maintenance requirements.

The Nickel Cadmium (NiCd) battery

The NiCd prefers fast charge to slow charge and pulse charge to DC charge. All other chemistries prefer a shallow discharge and moderate load currents. The NiCd is a strong and silent worker; hard labor poses no problem. In fact, the NiCd is the only battery type that performs well under rigorous working conditions. It does not like to be pampered by sitting in chargers for days and being used only occasionally for brief periods. A periodic full discharge is so important that, if omitted, large crystals will form on the cell plates (also referred to as memory) and the NiCd will gradually lose its performance.

Among rechargeable batteries, NiCd remains a popular choice for applications such as two-way radios, emergency medical equipment and power tools. Batteries with higher energy densities and less toxic metals are causing a diversion from NiCd to newer technologies.

Advantages and Limitations of NiCd Batteries
Advantages	Fast and simple charge — even after prolonged storage. High number of charge/discharge cycles — if properly maintained, the NiCd provides over 1000 charge/discharge cycles. Good load performance — the NiCd allows recharging at low temperatures. Long shelf life – in any state-of-charge. Simple storage and transportation — most airfreight companies accept the NiCd without special conditions. Good low temperature performance. Forgiving if abused — the NiCd is one of the most rugged rechargeable batteries. Economically priced — the NiCd is the lowest cost battery in terms of cost per cycle. Available in a wide range of sizes and performance options — most NiCd cells are cylindrical.
Limitations	Relatively low energy density — compared with newer systems. Memory effect — the NiCd must periodically be exercised to prevent memory. Environmentally unfriendly — the NiCd contains toxic metals. Some countries are limiting the use of the NiCd battery. Has relatively high self-discharge — needs recharging after storage.

Figure 2: Advantages and limitations of NiCd batteries.

The Nickel-Metal Hydride (NiMH) battery

Research of the NiMH system started in the 1970s as a means of discovering how to store hydrogen for the nickel hydrogen battery. Today, nickel hydrogen batteries are mainly used for satellite applications. They are bulky, contain high-pressure steel canisters and cost thousands of dollars per cell.

In the early experimental days of the NiMH battery, the metal hydride alloys were unstable in the cell environment and the desired performance characteristics could not be achieved. As a result, the development of the NiMH slowed down. New hydride alloys were developed in the 1980s that were stable enough for use in a cell. Since the late 1980s, NiMH has steadily improved.

The success of the NiMH has been driven by its high energy density and the use of environmentally friendly metals. The modern NiMH offers up to 40 percent higher energy density compared to NiCd. There is potential for yet higher capacities, but not without some negative side effects.

The NiMH is less durable than the NiCd. Cycling under heavy load and storage at high temperature reduces the service life. The NiMH suffers from high self-discharge, which is considerably greater than that of the NiCd.

The NiMH has been replacing the NiCd in markets such as wireless communications and mobile computing. In many parts of the world, the buyer is encouraged to use NiMH rather than NiCd batteries. This is due to environmental concerns about careless disposal of the spent battery.

Experts agree that the NiMH has greatly improved over the years, but limitations remain. Most of the shortcomings are native to the nickel-based technology and are shared with the NiCd battery. It is widely accepted that NiMH is an interim step to lithium battery technology.

Advantages and Limitations of NiMH Batteries
Advantages	30 – 40 percent higher capacity over a standard NiCd. The NiMH has potential for yet higher energy densities. Less prone to memory than the NiCd. Periodic exercise cycles are required less often. Simple storage and transportation — transportation conditions are not subject to regulatory control. Environmentally friendly — contains only mild toxins; profitable for recycling.
Limitations	Limited service life — if repeatedly deep cycled, especially at high load currents, the performance starts to deteriorate after 200 to 300 cycles. Shallow rather than deep discharge cycles are preferred. Limited discharge current — although a NiMH battery is capable of delivering high discharge currents, repeated discharges with high load currents reduces the battery’s cycle life. Best results are achieved with load currents of 0.2C to 0.5C (one-fifth to one-half of the rated capacity). More complex charge algorithm needed — the NiMH generates more heat during charge and requires a longer charge time than the NiCd. The trickle charge is critical and must be controlled carefully. High self-discharge — the NiMH has about 50 percent higher self-discharge compared to the NiCd. New chemical additives improve the self-discharge but at the expense of lower energy density. Performance degrades if stored at elevated temperatures — the NiMH should be stored in a cool place and at a state-of-charge of about 40 percent. High maintenance — battery requires regular full discharge to prevent crystalline formation. About 20 percent more expensive than NiCd — NiMH batteries designed for high current draw are more expensive than the regular version.

Figure 3: Advantages and limitations of NiMH batteries

The Lead Acid battery

Invented by the French physician Gaston Planté in 1859, lead acid was the first rechargeable battery for commercial use. Today, the flooded lead acid battery is used in automobiles, forklifts and large uninterruptible power supply (UPS) systems.

During the mid 1970s, researchers developed a maintenance-free lead acid battery that could operate in any position. The liquid electrolyte was transformed into moistened separators and the enclosure was sealed. Safety valves were added to allow venting of gas during charge and discharge.

Driven by different applications, two battery designations emerged. They are the small sealed lead acid (SLA), also known under the brand name of Gelcell, and the large valve regulated lead acid (VRLA). Technically, both batteries are the same. (Engineers may argue that the word ‘sealed lead acid’ is a misnomer because no lead acid battery can be totally sealed.) Because of our emphasis on portable batteries, we focus on the SLA.

Unlike the flooded lead acid battery, both the SLA and VRLA are designed with a low over-voltage potential to prohibit the battery from reaching its gas-generating potential during charge. Excess charging would cause gassing and water depletion. Consequently, these batteries can never be charged to their full potential.

The lead acid is not subject to memory. Leaving the battery on float charge for a prolonged time does not cause damage. The battery’s charge retention is best among rechargeable batteries. Whereas the NiCd self-discharges approximately 40 percent of its stored energy in three months, the SLA self-discharges the same amount in one year. The SLA is relatively inexpensive to purchase but the operational costs can be more expensive than the NiCd if full cycles are required on a repetitive basis.

The SLA does not lend itself to fast charging — typical charge times are 8 to 16 hours. The SLA must always be stored in a charged state. Leaving the battery in a discharged condition causes sulfation, a condition that makes the battery difficult, if not impossible, to recharge.

Unlike the NiCd, the SLA does not like deep cycling. A full discharge causes extra strain and each cycle robs the battery of a small amount of capacity. This wear-down characteristic also applies to other battery chemistries in varying degrees. To prevent the battery from being stressed through repetitive deep discharge, a larger SLA battery is recommended.

Depending on the depth of discharge and operating temperature, the SLA provides 200 to 300 discharge/ charge cycles. The primary reason for its relatively short cycle life is grid corrosion of the positive electrode, depletion of the active material and expansion of the positive plates. These changes are most prevalent at higher operating temperatures. Cycling does not prevent or reverse the trend.

The optimum operating temperature for the SLA and VRLA battery is 25°C (77°F). As a rule of thumb, every 8°C (15°F) rise in temperature will cut the battery life in half. VRLA that would last for 10 years at 25°C will only be good for 5 years if operated at 33°C (95°F). The same battery would endure a little more than one year at a temperature of 42°C (107°F).

Among modern rechargeable batteries, the lead acid battery family has the lowest energy density, making it unsuitable for handheld devices that demand compact size. In addition, performance at low temperatures is poor.

The SLA is rated at a 5-hour discharge or 0.2C. Some batteries are even rated at a slow 20-hour discharge. Longer discharge times produce higher capacity readings. The SLA performs well on high pulse currents. During these pulses, discharge rates well in excess of 1C can be drawn.

In terms of disposal, the SLA is less harmful than the NiCd battery but the high lead content makes the SLA environmentally unfriendly.

Advantages and Limitations of Lead Acid Batteries
Advantages	Inexpensive and simple to manufacture — in terms of cost per watt hours, the SLA is the least expensive. Mature, reliable and well-understood technology — when used correctly, the SLA is durable and provides dependable service. Low self-discharge —the self-discharge rate is among the lowest in rechargeable batterysystems. Low maintenance requirements — no memory; no electrolyte to fill. Capable of high discharge rates.
Limitations	Cannot be stored in a discharged condition. Low energy density — poor weight-to-energy density limits use to stationary and wheeled applications. Allows only a limited number of full discharge cycles — well suited for standby applications that require only occasional deep discharges. Environmentally unfriendly — the electrolyte and the lead content can cause environmental damage. Transportation restrictions on flooded lead acid — there are environmental concerns regarding spillage in case of an accident. Thermal runaway can occur with improper charging.

Figure 4: Advantages and limitations of lead acid batteries.

The Lithium Ion battery

Pioneer work with the lithium battery began in 1912 under G.N. Lewis but it was not until the early 1970s that the first non-rechargeable lithium batteries became commercially available. Lithium is the lightest of all metals, has the greatest electrochemical potential and provides the largest energy density per weight.

Attempts to develop rechargeable lithium batteries followed in the 1980s, but failed due to safety problems. Because of the inherent instability of lithium metal, especially during charging, research shifted to a non-metallic lithium battery using lithium ions. Although slightly lower in energy density than lithium metal, the Li‑ion is safe, provided certain precautions are met when charging and discharging. In 1991, the Sony Corporation commercialized the first Li‑ion battery. Other manufacturers followed suit. Today, the Li‑ion is the fastest growing and most promising battery chemistry.

The energy density of the Li‑ion is typically twice that of the standard NiCd. Improvements in electrode active materials have the potential of increasing the energy density close to three times that of the NiCd. In addition to high capacity, the load characteristics are reasonably good and behave similarly to the NiCd in terms of discharge characteristics (similar shape of discharge profile, but different voltage). The flat discharge curve offers effective utilization of the stored power in a desirable voltage spectrum.

The high cell voltage allows battery packs with only one cell. Most of today’s mobile phones run on a single cell, an advantage that simplifies battery design. To maintain the same power, higher currents are drawn. Low cell resistance is important to allow unrestricted current flow during load pulses.

The Li‑ion is a low maintenance battery, an advantage that most other chemistries cannot claim. There is no memory and no scheduled cycling is required to prolong the battery’s life. In addition, the self-discharge is less than half compared to NiCd, making the Li‑ion well suited for modern fuel gauge applications. Li‑ion cells cause little harm when disposed.

Despite its overall advantages, Li‑ion also has its drawbacks. It is fragile and requires a protection circuit to maintain safe operation. Built into each pack, the protection circuit limits the peak voltage of each cell during charge and prevents the cell voltage from dropping too low on discharge. In addition, the cell temperature is monitored to prevent temperature extremes. The maximum charge and discharge current is limited to between 1C and 2C. With these precautions in place, the possibility of metallic lithium plating occurring due to overcharge is virtually eliminated.

Aging is a concern with most Li‑ion batteries and many manufacturers remain silent about this issue. Some capacity deterioration is noticeable after one year, whether the battery is in use or not. Over two or perhaps three years, the battery frequently fails. It should be noted that other chemistries also have age-related degenerative effects. This is especially true for the NiMH if exposed to high ambient temperatures.

Storing the battery in a cool place slows down the aging process of the Li‑ion (and other chemistries). Manufacturers recommend storage temperatures of 15°C (59°F). In addition, the battery should be partially charged during storage.

Manufacturers are constantly improving the chemistry of the Li‑ion battery. New and enhanced chemical combinations are introduced every six months or so. With such rapid progress, it is difficult to assess how well the revised battery will age.

The most economical Li-ion battery in terms of cost-to-energy ratio is the cylindrical 18650 cell. This cell is used for mobile computing and other applications that do not demand ultra-thin geometry. If a slimmer pack is required (thinner than 18 mm), the prismatic Li‑ion cell is the best choice. There are no gains in energy density over the 18650, however, the cost of obtaining the same energy may double.

For ultra-slim geometry (less than 4 mm), the only choice is Li‑ion polymer. This is the most expensive system in terms of cost-to-energy ratio. There are no gains in energy density and the durability is inferior to the rugged 18560 cell.

Advantages and Limitations of Li-ion Batteries
Advantages	High energy density — potential for yet higher capacities. Relatively low self-discharge — self-discharge is less than half that of NiCd and NiMH. Low Maintenance — no periodic discharge is needed; no memory.
Limitations	Requires protection circuit — protection circuit limits voltage and current. Battery is safe if not provoked. Subject to aging, even if not in use — storing the battery in a cool place and at 40 percent state-of-charge reduces the aging effect. Moderate discharge current. Subject to transportation regulations — shipment of larger quantities of Li-ion batteries may be subject to regulatory control. This restriction does not apply to personal carry-on batteries. Expensive to manufacture — about 40 percent higher in cost than NiCd. Better manufacturing techniques and replacement of rare metals with lower cost alternatives will likely reduce the price. Not fully mature — changes in metal and chemical combinations affect battery test results, especially with some quick test methods.

Figure 5: Advantages and limitations of Li?ion batteries

The Lithium Polymer battery

The Li-polymer differentiates itself from other battery systems in the type of electrolyte used. The original design, dating back to the 1970s, uses a dry solid polymer electrolyte. This electrolyte resembles a plastic-like film that does not conduct electricity but allows an exchange of ions (electrically charged atoms or groups of atoms). The polymer electrolyte replaces the traditional porous separator, which is soaked with electrolyte.

The dry polymer design offers simplifications with respect to fabrication, ruggedness, safety and thin-profile geometry. There is no danger of flammability because no liquid or gelled electrolyte is used. With a cell thickness measuring as little as one millimeter (0.039 inches), equipment designers are left to their own imagination in terms of form, shape and size.

Unfortunately, the dry Li-polymer suffers from poor conductivity. Internal resistance is too high and cannot deliver the current bursts needed for modern communication devices and spinning up the hard drives of mobile computing equipment. Heating the cell to 60°C (140°F) and higher increases the conductivity but this requirement is unsuitable for portable applications.

To make a small Li-polymer battery conductive, some gelled electrolyte has been added. Most of the commercial Li-polymer batteries used today for mobile phones are a hybrid and contain gelled electrolyte. The correct term for this system is Lithium Ion Polymer. For promotional reasons, most battery manufacturers mark the battery simply as Li-polymer. Since the hybrid lithium polymer is the only functioning polymer battery for portable use today, we will focus on this chemistry.

With gelled electrolyte added, what then is the difference between classic Li‑ion and Li‑ion polymer? Although the characteristics and performance of the two systems are very similar, the Li‑ion polymer is unique in that solid electrolyte replaces the porous separator. The gelled electrolyte is simply added to enhance ion conductivity.

Technical difficulties and delays in volume manufacturing have deferred the introduction of the Li‑ion polymer battery. In addition, the promised superiority of the Li‑ion polymer has not yet been realized. No improvements in capacity gains are achieved — in fact, the capacity is slightly less than that of the standard Li‑ion battery. For the present, there is no cost advantage. The major reason for switching to the Li-ion polymer is form factor. It allows wafer-thin geometries, a style that is demanded by the highly competitive mobile phone industry.

Advantages and Limitations of Li-ion Polymer Batteries
Advantages	Very low profile — batteries that resemble the profile of a credit card are feasible. Flexible form factor — manufacturers are not bound by standard cell formats. With high volume, any reasonable size can be produced economically. Light weight – gelled rather than liquid electrolytes enable simplified packaging, in some cases eliminating the metal shell. Improved safety — more resistant to overcharge; less chance for electrolyte leakage.
Limitations	Lower energy density and decreased cycle count compared to Li-ion — potential for improvements exist. Expensive to manufacture — once mass-produced, the Li-ion polymer has the potential for lower cost. Reduced control circuit offsets higher manufacturing costs.

Figure 6: Advantages and limitations of Li?ion polymer batteries.

Summary

During the last few decades, rechargeable batteries have made only moderate improvements in terms of higher capacity and smaller size. Compared with the vast advancements in areas such as microelectronics, the lack of progress in battery technology is apparent. Consider a computer memory core of the sixties and compare it with a modern microchip of the same byte count. What once measured a cubic foot now sits in a tiny chip. A comparable size reduction would literally shrink a heavy-duty car battery to the size of a coin. Since batteries are still based on an electrochemical process, a car battery the size of a coin may not be possible using our current techniques.

Research has brought about a variety of battery chemistries, each offering distinct advantages but none providing a fully satisfactory solution. With today’s increased selection, however, better choices can be made to suit a specific user application.

source: http://www.buchmann.ca/Article4-Page1.asp

Laptops tend to lose their charm quickly when you’re constantly looking for the nearest power outlet to charge up. How do you keep your battery going for as long as possible? Here are 15 easy ways to do so.

1. Defrag regularly - The faster your hard drive does its work - less demand you are going to put on the hard drive and your battery. Make your hard drive as efficient as possible by defragging it regularly. (but not while it’s on battery of course!) Mac OSX is better built to handle fragmentation so it may not be very applicable for Apple systems.

2. Dim your screen - Most laptops come with the ability to dim your laptop screen. Some even come with ways to modify CPU and cooling performance. Cut them down to the lowest level you can tolerate to squeeze out some extra battery juice.

3. Cut down on programs running in the background. Itunes, Desktop Search, etc. All these add to the CPU load and cut down battery life. Shut down everything that isn’t crucial when you’re on battery.

4. Cut down external devices - USB devices (including your mouse) & WiFi drain down your laptop battery. Remove or shut them down when not in use. It goes without saying that charging other devices (like your iPod) with your laptop when on battery is a surefire way of quickly wiping out the charge on your laptop battery.

5. Add more RAM - This will allow you to process more with the memory your laptop has, rather than relying on virtual memory. Virtual memory results in hard drive use, and is much less power efficient. Note that adding more RAM will consume more energy, so this is most applicable if you do need to run memory intensive programs which actually require heavy usage of virtual memory.

6. Run off a hard drive rather than CD/DVD - As power consuming as hard drives are, CD and DVD drives are worse. Even having one in the drive can be power consuming. They spin, taking power, even when they?re not actively being used. Wherever possible, try to run on virtual drives using programs like Alcohol 120% rather than optical ones.

7. Keep the battery contacts clean: Clean your battery’s metal contacts every couple of months with a cloth moistened with rubbing alcohol. This keeps the transfer of power from your battery more efficient.

8. Take care of your battery - Exercise the Battery. Do not leave a charged battery dormant for long periods of time. Once charged, you should at least use the battery at least once every two to three weeks. Also, do not let a Li-On battery completely discharge. (Discharing is only for older batteries with memory effects)

9. Hibernate not standby - Although placing a laptop in standby mode saves some power and you can instantly resume where you left off, it doesn’t save anywhere as much power as the hibernate function does. Hibernating a PC will actually save your PC’s state as it is, and completely shut itself down.

10. Keep operating temperature down - Your laptop operates more efficiently when it’s cooler. Clean out your air vents with a cloth or keyboard cleaner, or refer to some extra tips by LapTopMag.com.

11. Set up and optimize your power options - Go to ‘Power Options’ in your windows control panel and set it up so that power usage is optimized (Select the ‘max battery’ for maximum effect).

12. Don’t multitask - Do one thing at a time when you’re on battery. Rather than working on a spreadsheet, letting your email client run in the background and listening to your latest set of MP3’s, set your mind to one thing only. If you don’t you’ll only drain out your batteries before anything gets completed!

13. Go easy on the PC demands - The more you demand from your PC. Passive activities like email and word processing consume much less power than gaming or playing a DVD. If you’ve got a single battery charge - pick your priorities wisely.

14. Get yourself a more efficient laptop - Laptops are getting more and more efficient in nature to the point where some manufacturers are talking about all day long batteries. Picking up a newer more efficient laptop to replace an aging one is usually a quick fix.

15. Prevent the Memory Effect - If you’re using a very old laptop, you’ll want to prevent the ‘memory effect’ - Keep the battery healthy by fully charging and then fully discharging it at least once every two to three weeks. Exceptions to the rule are Li-Ion batteries (which most laptops have) which do not suffer from the memory effect.

Bonus Tip #1: Turn off the autosave function. MS-Word’s and Excel’s autosave functions are great but because they keep saving regular intervals, they work your hard driver harder than it may have to. If you plan to do this, you may want to turn it back on as the battery runs low. While it saves battery life in the beginning, you will want to make sure your work is saved when your battery dies.

Bonus Tip #2: Lower the graphics use. You can do this by changing the screen resolution and shutting off fancy graphic drivers. Graphics cards (video cards) use as much or more power today as hard disks - Thanks Andrew

Update 7/7/07: Bonus Tip #1 to give caution about turning off autosave, tip #8 to change information about discharging batteries - thanks to all who pointed it out. Added Bonus tip #2, Tip #1 to add in clause in regards to Mac OSX, Tip #1 about the spinning of hard drives - thanks to all who pointed it out

What are your experiences with laptop batteries? Share them with us in the comments!

Source: http://www.friedbeef.com/2007/07/01/top-15-ways-to-extend-your-laptop-battery-life/

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