Thursday, January 01, 2004

More recommendations on the care and feeding of LiOn batteries

iPod Battery FAQ
Q: What is the best way to handle charging/discharging/storage of lithium ion batteries?

... Lithium ion batteries are good for 300-500 charge/discharge cycles. A 'charge/discharge' cycle generally consists of an extended charging period, and an extended discharging period. A quick charge, listening for 30 minutes, and charging again, for example, does not constitute a full 'charge/discharge cycle', but could rather be considered a portion of one.

Also, many, many factors affect how much you get out of each charge, as well as how long the battery will last overall. The main factors include charging patterns, the routine amount of discharge (i.e., Do you use it until it dies? Use it for an hour or two and recharge?), temperature, storage, usage frequency, etc. Lithium ion batteries do not take kindly to frequent full or complete discharges. When possible, the optimal usage pattern - for any lithium ion battery - is a partial discharge, followed by recharging. A partial discharge can be anything less than a full discharge. However, an occasional full discharge is desirable (e.g., once every 30 charges) to calibrate the battery. Lithium ion batteries do not significantly degrade, or develop 'memory', even if charged at irregular intervals; irregular charging is acceptable. An iPod can also safely be attached to external power for extended periods of time. (For extremely extended periods of time, such as months, the battery will essentially be the same as if it were in 'storage'; lithium ion batteries do not store well for extended periods of time at full charge. However, there is no way around this under these circumstances.) When possible, always use the AC adapter (or vehicle adapter) for extended charging, not a FireWire cable attached to a computer.

If you will be storing your iPod for an extended period of time (i.e., weeks to months), it is recommended to store the unit in a cool place at about 40% charge. The most harmful combination for storage is full charge at high temperature (i.e., in a hot car for a couple of weeks).

This matches everything I've read and practice. I think it's equally true for an iBook. My sense is that only SONY truly has true mastery of LiOn batteries -- they developed the core technology and I suspect they may have some unique patents or skill with them -- Apple and PalmOne are not in teh same class.

I try to run in the 40-100% charge range. It's good to know however than an iPod can be happily left in its powered cradle -- assuming the cradle is connected to the wall charger.

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