[Jazzbass]

Electrical troubleshooting 101:

Either you're battery isn't getting charged (alternator problem) or something is draining current while the car is off. To test for the latter:

Get an ammeter. Hook it up between the battery and the car while the car is off. See how much current you are drawing - it should be low, less than an amp. If you're draining your battery that fast, it won't be low. Then, start pulling fuses one at a time until the current drain goes away. If you're lucky, one of the fused circuits will contain the cause of the current drain.

Now, find out what's on that circuit. Plug the fuse back in. Unplug items on the circuit until the current drain goes away. There is the cause of your dead battery. Hope its not your DME box or something similarly expensive.