Maybe it's just starting to die? When mine was dying I saw a lot of weird moments when a fully charged battery would go to 20-30% in a matter of minutes. Literally like 10mins and it's almost empty.
A normal battery shouldn't drain more than 1-3% overnight.
Originally Posted by Ziggler Mark
If you constantly keep a charger hooked up to the laptop while you're at home or whatever, though, it wreaks havoc on long-term battery life.
Sure does. My new battery died in 12 months cause I was too lazy to take it out when at home and hooked up to charger.