Actually, leaving it on the computer won't "overcharge" or do something like that (as far as I know, notebooks use Lithium ions batteries). They have a circuit that don't allow that. That's what I've read on batteryuniversity.com.
However, one thing I realized is that if you leave it on the computer for a long time while using on AC, you will act as storing it at 100%, and you should store it at around 40-45% of the charge, if i remember... So, it does not overcharge, but wears more if stored with a full charge.
My only doubt is: since the battery, on the notebook at AC, is connected to the power supply, does it act as storing? or does this "40% rule" only apply when storing it unplugged?? Can someone tell me?