If you consistently use your laptop just a couple of hours at a time on battery power, and then connect it to the AC adapter to recharge it, over the period of a few months the battery will “lose track” of how much charge it really holds. This is called shallow chargeing and not recommended.

Try turning the laptop off, removing the battery and leaving it out to slowly drain down and reinsert several days later. When reinserted, does the laptop still read 100% battery? If so, consider recalibrating the BIOS. If not, leave the battery in and the laptop on with battery power only and let the battery drain for hours. Once drained, try to recharge the battery to re-condition it. Do a recharge, discharge 2 more times to condition well.

Some notebooks have a battery calibration feature in the BIOS settings menu - consult the paper or on-line manual that accompanied your system for details or try suggestion below.

http://www.batteryfuel.com

For more details follow the instructions below from RM.com

Recalibrate the Smart Battery

1. Check that the system is on AC power.
2. Switch off the system.
3. Leave the system overnight (eight hours) to charge.
4. Switch on the system and check that the system is still on AC power.
5. In Control Panel, Performance and Maintenance, Power Options, and change the Power Scheme to Always On. Then change the ‘Running on Batteries’ settings to all say ‘Never’ and click on ‘OK’.
6. Click on the Power Meter tab, and check that the battery is at 100%.
7. Now remove the AC adapter plug and switch off the AC adapter power at the mains supply.
8. Time how long the system remains powered. You can use a utility to log the time to the hard disk at regular intervals.
9. After the system has switched itself off (usually by a self-controlled ‘Shutdown’), connect the AC adapter again and switch on the power to recharge the battery.
10. Leave for eight hours to fully recharge.
Credited Source:
RM.com
http://www.batteryfuel.com
http://www.batteryfuel.com/faq1.html
BatteryFuel is an eCommerce reseller, since 2002, of replacement batteries for laptops, cell-phones, camcorders, digital cameras and many more electronic devices. You can find many name brand replacement batteries and adapters like Acer, Apple, Compaq, Sony, Toshiba, Dell, Hewlett Packard HP at their online store.