Most laptops now use lithium ion (LiIon) batteries. LiIons should be managed differently from the NiCad or NiMH batteries used in older laptops. In particular, LiIons should not be run all the way down to prevent "memory effect". First, they don't have a memory effect, and second, running them down tends to reduce their capacity. If the laptop does not need the battery it should be run to about 40% charge and stored in a cool place. LiIon batteries go bad whether used or not, so only buy new LiIons. Typical life is 2-3 years.
Why are iBook and Powerbook batteries so expensive? Part of the reason is that LiIon batteries can do bad things if they overheat (creation of Lithum metal which "burns" in water, chance of fire). So LiIon battery packs have an internal circuit to prevent overcharging (which would cause them to overheat). There can be several functions for the protection circuit, including shutting it down in case of over charging, when the voltage drops to a predefined level, or if it thinks the battery is otherwise damaged.
Problems with the power circuit can cause a "good" battery to shut down. The recent post about fixing iPod batteries likely had to do with re-setting something in the battery protection circuit that caused it to shut the battery off early. Isidor Buchmann's Batteries in a Portable World site talks about methods some have used to try to reset the protection circuit on batteries that seem to have died young.
Trying to reset a LiIon protection circuit is dangerous to try yourself - you could end up with a nasty fire. Plus the electrolyte is flammable and caustic, so it needs to be well packaged to make a spill unlikely, even if you do manage to overheat it.
All this costs, which helps explain the price of the batteries...
[robg adds: I know this isn't exactly an OS X hint, but battery questions seem to come up a lot. The referenced website has to be one of the most throrough I've ever seen; the online book goes into more detail than I thought possible on the subject! The remainder of this hint has some snippets from the book, along with URLs to the pages the snippets were taken from. Read on if you'd like to get a feel for what's on the site, or just go visit Isidor's website and read the whole thing online.]
Summary of excerpts on using LiIons from Batteries in a Portable World:
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 and NiMH, making the Li-ion well suited for modern fuel gauge applications.
Li-ion offers internal resistance characteristics that are between those of NiMH and NiCd. Usage does not contribute much to the increase in resistance, but aging does. The typical life span of a Li-ion battery is two to three years, whether it is used or not. Cool storage and keeping the battery in a partially charged state when not in use retard the aging process.
The internal resistance of the Li-ion batteries cannot be improved with cycling. The cell oxidation, which causes high resistance, is non-reversible. The ultimate cause of failure is high internal resistance. Energy may still be present in the battery, but it can no longer be delivered due to poor conductivity.
The loss of charge acceptance of the Li-ion/polymer batteries is due to cell oxidation, which occurs naturally during use and as part of aging. Li-ion batteries cannot be restored with cycling or any other external means. The capacity loss is permanent because the metals used in the cells are designated to run for a specific time only and are being consumed during their service life.
The Li-ion battery has a time clock that starts ticking as soon as the battery leaves the factory. The electrolyte slowly 'eats up' the positive plate and the electrolyte decays. This chemical change causes the internal resistance to increase. In time, the cell resistance raises to a point where the battery can no longer deliver the energy, although it may still be retained in the battery.
In addition to cycling, the battery ages even if not used. The amount of permanent capacity loss the battery suffers during storage is governed by the SoC and temperature. For best results, keep the battery cool. In addition, store the battery at a 40 percent charge level. Never fully charge or discharge the battery before storage. The 40 percent charge assures a stable condition even if self-discharge robs some of the battery's energy. Most battery manufacturers store Li-ion batteries at 15°C (59°F) and at 40 percent charge.
Lithium-based batteries have a defined age limit. Once the anticipated cycles have been delivered, no method exists to improve the battery. The main reason for failure is high internal resistance caused by oxidation. Operating the battery at elevated temperatures will momentarily reduce this condition. When the temperature normalizes, the condition of high internal resistance returns.
The speed of oxidation depends on the storage temperature and the battery's charge state. Keeping the battery in a cool place can prolong its life. The Li-ion battery should be stored at 40 percent rather than full-charge state.
An increasing number of modern batteries fall prey to the cut-off problem induced by a deep discharge. This is especially evident on Li-ion batteries for mobile phones. If discharged below 2.5V/cell, the internal protection circuit often opens. Many chargers cannot apply a recharge and the battery appears to be dead.
Lithium-based batteries have a defined age limit. Once the anticipated cycles have been delivered, no method exists to improve the battery. The main reason for failure is high internal resistance caused by oxidation. Operating the battery at elevated temperatures will momentarily reduce this condition. When the temperature normalizes, the condition of high internal resistance returns.
The speed of oxidation depends on the storage temperature and the battery's charge state. Keeping the battery in a cool place can prolong its life. The Li-ion battery should be stored at 40 percent rather than full-charge state.
An increasing number of modern batteries fall prey to the cut-off problem induced by a deep discharge. This is especially evident on Li-ion batteries for mobile phones. If discharged below 2.5V/cell, the internal protection circuit often opens. Many chargers cannot apply a recharge and the battery appears to be dead.
... a Li-ion performs better at high temperatures. Elevated temperatures temporarily counteracts the battery's internal resistance, which is a result of aging. The energy gain is short-lived because elevated temperature promotes aging by further increasing the internal resistance.
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 maximum charge and discharge current is limited and the cell temperature is monitored to prevent temperature extremes. 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. For unknown reasons, battery manufacturers are 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 mentioned 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 only be partially charged when in storage.
Extended storage is not recommended for Li-ion batteries. Instead, packs should be rotated. The buyer should be aware of the manufacturing date when purchasing a replacement Li-ion battery. Unfortunately, this information is often encoded in an encrypted serial number and is only available to the manufacturer.
The Li-ion does not like prolonged storage. Irreversible capacity loss occurs after 6 to 12 months, especially if the battery is stored at full charge and at warm temperatures.
The recommended storage temperature of a lithium-based battery is 15°C (59°F) or less. A charge level of 40 percent allows for some self-discharge that naturally occurs; and 15°C is a practical and economical storage temperature that can be achieved without expensive climate control systems.
The self-discharge of the Li-ion battery is five percent in the first 24 hours after charge and averages 1 to 2 percent per month thereafter. In addition to the natural self-discharge through the chemical cell, the safety circuit draws as much as 3 percent per month. High cycle count and aging has little effect on self-discharge on lithium-based batteries.
The charge time of all Li-ion batteries, when charged at a 1C initial current, is about 3 hours. The battery remains cool during charge. Full charge is attained after the voltage has reached the upper voltage threshold and the current has dropped and leveled off at about 3 percent of the nominal charge current.
Increasing the charge current on a Li-ion charger does not shorten the charge time by much. Although the voltage peak is reached quicker with higher current, the topping charge will take longer. Figure 4-5 shows the voltage and current signature of a charger as the Li-ion cell passes through stage one and two.
Some chargers claim to fast-charge a Li-ion battery in one hour or less. Such a charger eliminates stage 2 and goes directly to 'ready' once the voltage threshold is reached at the end of stage 1. The charge level at this point is about 70 percent. The topping charge typically takes twice as long as the initial charge.
No trickle charge is applied because the Li-ion is unable to absorb overcharge. Trickle charge could cause plating of metallic lithium, a condition that renders the cell unstable. Instead, a brief topping charge is applied to compensate for the small amount of self-discharge the battery and its protective circuit consume.
What if a battery is inadvertently overcharged? Li-ion batteries are designed to operate safely within their normal operating voltage but become increasingly unstable if charged to higher voltages. On a charge voltage above 4.30V, the cell causes lithium metal plating on the anode. In addition, the cathode material becomes an oxidizing agent, loses stability and releases oxygen. Overcharging causes the cell to heat up.
The Li-ion batteries offer good cold and hot temperature charging performance. Some cells allow charging at 1C from 0°C to 45°C (32°F to 113°F). Most Li-ion cells prefer a lower charge current when the temperature gets down to 5°C (41°F) or colder. Charging below freezing must be avoided because plating of lithium metal could occur.
Li-ion/polymer batteries are electronically protected against high discharge currents . Depending on battery type, the discharge current is limited somewhere between 1C and 2C. This protection makes the Li-ion unsuitable for biomedical equipment, power tools and high-wattage transceivers. These applications are commonly reserved for the NiCd battery.
The Li-ion typically discharges to 3.0V/cell. The spinel and coke versions can be discharged to 2.5V/cell. The lower end-of-discharge voltage gains a few extra percentage points. Since the equipment manufacturers cannot specify which battery type may be used, most equipment is designed for a three-volt cut-off.
Caution should be exercised not to discharge a lithium-based battery too low. Discharging a lithium-based battery below 2.5V may cut off the battery's protection circuit. Not all chargers accommodate a recharge on batteries that have gone to sleep because of low voltage.
Some Li-ion batteries feature an ultra-low voltage cut-off that permanently disconnects the pack if a cell dips below 1.5V. This precaution prohibits recharge if a battery has dwelled in an illegal voltage state. A very deep discharge may cause the formation of copper shunt, which can lead to a partial or total electrical short. The same occurs if the cell is driven into negative polarity and is kept in that state for a while. A fully discharged battery should be charged at 0.1C. Charging a battery with a copper shunt at the 1C rate would cause excessive heat. Such a battery should be removed from service.
The internal protection circuit of lithium-based batteries may be the cause of some problems. For safety reasons, many of these batteries do not allow a recharge if the battery has been discharged below 2.5V/cell. If discharged close to 2.5V and the battery is not recharged for a while, self-discharge further discharges the pack below the 2.5V level. If, at this time, the battery is put into the charger, nothing may happen. The battery appears to have an open circuit and the user consequently demands a replacement.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20030314081843218