The Tekblog

One of the worst things you can do for a battery is to never use it; that is, leave your device plugged in all the time. I see a lot of people who primarily use their laptop at their desk and very rarely use the battery.

At a 100% charge level, a typical Lithium-Ion laptop battery that is full most of the time at 77°F will irreversibly lose approximately 20% capacity per year. However, a battery in a poorly ventilated laptop may be subject to a prolonged exposure to much higher temperatures, which will significantly shorten its life. Different storage temperatures produce different loss results: 6% loss at 32°F, 20% at 77°F, and 35% at 104°F. When stored at 40%–60% charge level, the capacity loss is reduced to 2%, 4%, 15% at 32, 77 and 104 degrees respectively.

Guidelines for prolonging Lithium-Ion battery life

• Like many rechargeable batteries, lithium-ion batteries should be charged early and often. However, if they are not used for a long time, they should be brought to a charge level of around 40%–60%
• Lithium-ion batteries should not be frequently fully discharged and recharged ("deep-cycled"), but this may be necessary after about every 30th recharge to recalibrate any electronic charge monitor (e.g. a battery meter). This allows the monitoring electronics to more accurately estimate battery charge. This has nothing to do with the memory effect.
• Li-ion batteries should never be depleted 100%, unless you are calibrating the battery, or below their minimum voltage, 2.4 V to 3.0 V per cell.
• Li-ion batteries should be kept cool. Ideally they are stored in a refrigerator. Aging will take its toll much faster at high temperatures. The high temperatures found in cars cause lithium-ion batteries to degrade rapidly.
• Li-ion batteries should not be frozen (most lithium-ion battery electrolytes freeze at approximately −40 °C; however, this is much colder than the lowest temperature reached by household freezers).
• Li-ion batteries should be bought only when needed, because the aging process begins as soon as the battery is manufactured.
• When using a notebook computer running from fixed line power over extended periods, consider removing the battery and storing it in a cool place so that it is not affected by the heat produced by the computer.

Most laptops come with a battery calibration utility that you can run and it will drain and recharge the battery. This will help the laptop to calculate the correct runtime of the battery as reported by Windows (or Mac and Linux for that matter).

I hope this is helpful…

-Justin

For a more comprehensive guide > http://batteryuniversity.com/parttwo.htm