|Originally posted by NightShade737
NiMH wouldnt be a good idea as while the battery life decreases the output voltage also decreases meaning that there may not be enough power to drive the laptop after a short amount of time, or you may start getting side effects.
It will charge up to a proper voltage, but then run for 20 minutes and drop to below nominal very quickly.
Nihms are easily recoverable, you can recondition them often, and zap them to break up internal shorts (quick charge of unfiltered 12volts for 1-2seconds)
Lithium Ion batts are also not very suited to high current draw, hence you would have to design the battery to prevent overloading cells (at least). The capacity of a LiIon increases when discharge current decreases.