The Li-ion battery should be stored at 40 percent rather than full-charge state

May 31, 2011 - PRLog -- Laptop batteries have finite life spans. Whether you use the power cord or remove the battery it will lengthen the life of the battery.

Li-Ion laptop battery lifespan is approximately 1,000 charge cycles, http://www.happybattery.com.au/laptop-battery/Hp/pavilion-dv6000.htm   Hp pavilion dv6000 battery
or 2-4 years under normal operating conditions.

Keeping the battery in a cool place can prolong its life but not in a period of extended storage. The Li-ion battery should be stored at 40 percent rather than full-charge state.
The battery ages even if not used. 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.
http://www.happybattery.com.au/laptop-battery/Hp/pavilion-dv9700.htm   Hp pavilion dv9700 battery

Keeping a laptop battery on constant charge and never using it is not good for the laptop battery. Run the battery down and recharging it at least once every month.
The quest for the more perfect battery for portable electronics continues into 2009. Energizer said it will showcase at the Consumer Electronics Show in early January a new battery to power devices which provides "greater run times" http://www.happybattery.com.au   laptop battery
and enables "smaller devices."
The Energizer Zinc Air Prismatic battery, said the company, will be targeted towards manufacturers. It reportedly offers "up to three times (3X) more" life than "similarly sized alkaline or lithium ion batteries" while remaining in a very thin size. There aren't many more details know yet, but you can read about this upcoming battery.

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One of the worst things that can happen while working on a laptop is to have your Laptop Battery die mid-project. To avoid this, it's good to know how much life your battery has left in it.