i can say from experience that if you arent smart with your laptop batteries, you will ruin them...
i had an old Sony Vaio back in the day, and i would always leave my battery in, with the AC power plugged in, then disconnect for a bit, then plug back in... over and over...
and after a while, i started noticing my battery life had taken a plunge... it got to the point where my battery would last about 20min before dying and i had to order a new one before someone told me this general rule:
drain it almost all the way down, then charge it all the way up... always
havent had any problems since then... same rule applies for almost all rechargeable batteries, from my understanding...
now i dont know much about the difference between Li-Ion or NiCH or w/e... but i do know that if you constantly recharge a semi-full battery... odds are good youll kill it...
check out some of those 'caring for you battery' guides or w/e, that people posted... some good info there... good luck
- RK