Originally Posted by Goldwing
Could just be a bad battery -- sediment shorted out a cell or a plate crumbled. Check your terminals and make sure they are clean. Take it to an Autozone for a free alternator and battery check. Check the voltage across the terminals with the fully charged battery disconnected (should be 13.2) and then when it is connected to make sure nothing is drawing current. Oledoc2u, if a teeny GPS battery is drawing down that big car battery, then it's not a very good car battery. Yes, it could happen over weeks, but not within 12 hours. Especially when the cigar lighter powers down when the car is off (my A6 stays on all the time, and I often forget and leave the GPS and radar detector going for days and that battery is the original in a 2003!).