It could be a weak battery. What I want you to do is take the car to the parts store and have them load test the battery. If it is good, it will maintain a set voltage under a load. If weak, it will drop off. If the battery is good, I want you to check if there is a constant draw on it. If there is, remove one fuse at a time until the draw stops. THen we will have narrowed it down to a specific circuit.
Here is a how to for checking for draw:
https://www.2carpros.com/first_things/why_is_my_car_battery_dead_over_night.htm
If you want to test the battery yourself, here is how to do that:
https://www.2carpros.com/how_to/battery.htm
Let me know what you find. Honestly, if it dies that fast, chances are the battery is no good, but these test will help determine it.
Joe
Wednesday, January 13th, 2010 AT 9:17 PM