Laptop battery help

[rcracer]

Hi all

whats the best way to keep your laptop battery in good order, my last laptop battery lasted 30 mins or so i always run it from the power supply, the lappy i have now has a 6 cell battery and i can get 5 - 6 hrs from it but are unsure what to do when it is fully charged will it do any harm to keep running it on the mains , hope someone understands what i am getting at