the battery in my wife's Saturn just died last night. I jumped it, got it home and tested it it read 14.5v running. I then unplugged both negative and positive and it read 12.8v, normal. I left it overnight and checked it in the morning, it was down to 10.6v with nothing hooked up. Put in a new battery, end of problem.
What I'm getting at is you may not know until you fully unplug the battery, this will tell you if it's the battery no longer holding a charge or something in the car draining it.
