For information about available battery types, take a look at the Hardware Features chapter above.
Stephen Rothwell is currently integrating a patch that will add multiple battery support to the kernel APM.
From the mobile-update page (modified by WH): Discharge the battery. If your battery runs only for about 20 minutes, you probably suffer from memory effects. Most laptops do not discharge the battery properly. With low powered devices like old computer fans they can be discharged completely. This removes memory effects. You should do so even with LiIon batteries, though they don't suffer much from memory effect (the manual of an IBM™ Thinkpad says to cycle the batteries through a full charge/discharge cycle 3 times every few months or so).
Try this at your own risk! Make sure the voltage of the fans is compatible to your battery. It works for me.
In the US, this company has most batteries for anything and can rebuild many that are no longer manufactured: Batteries Plus, 2045 Pleasant Hill Road, Duluth, GA 30096 +1 770 495 1644.