A long discussion here found about 10% gain in battery lifespan so I won't repeat that.
One big downside is that you lose a big feature of your laptop. It will now crash on any AC power dip.
For me, I added a laptop cooling pad.
I was wondering why my lap top Compaq Preasrio V3000 left side of the computer was hot sometimes. Is it because its the battery or is it the hard drive? I was thinkign if i wasnt going anywhere just stationary should i remove the lap top battery and just let the power plug charged the lap top without the battery? Will that damage the lap top? I was wondering because i am confuse weather the battery is making it hot or its the hard drive being run to hard.