After sitting a full day (in freezing temp) I was surprised to find my car was completely dead (absolutely nothing when I turn the key). I realized the dome light switch was on, so I began charging the battery. However the needle was more toward the left (5 amps), which I believe means the battery is mostly charged already. I charged it for only about 20 minutes, then I turned on the headlights and they worked, then the car started up fine. What could have caused this ?

Cars & Trucks - Buick - Century - 1999 Buick Century