An overview of laptop battery technology

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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:

  • There is no memory and no scheduled cycling is required to prolong the battery's life.
  • The typical life span of a Li-ion battery is two to three years, whether it is used or not.
  • The internal resistance of the Li-ion batteries cannot be improved with cycling. The cell oxidation, which causes high resistance, is non-reversible. 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.
  • 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.

Simple Guidelines:

  • Charge the Li-ion often, except before a long storage.
  • Store at about 40% charge in a cool place
  • Avoid repeated deep discharges.
  • Keep the Li-ion battery cool.
  • Prevent storage in a hot car.
  • Never freeze a battery.
  • If your laptop is capable of running without a battery and fixed power is used most of the time, remove the battery and store it in a cool place.
  • Avoid purchasing spare Li-ion batteries for later use.
  • Observe manufacturing date when purchasing.
  • Do not buy old stock, even if sold at clearance prices.

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An overview of laptop battery technology

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