I'd suggest obtaining the current being drawn from the battery while the car isn't running. Put a meter between the battery + and the terminal connector.
The reading should be pretty low, almost nothing really.
Take out each fuse one by one and see if the reading changes. If it does, see what the fuse is for and there you have your fault?
If you have any audio amps, maybe one of those is running all the time? I had that problem on a car once, battery lasted a few hours then dead. Just a thought.
