If you have a drain in the electrical system that is causing the battery to discharge, here is how you can find the trouble...

Remove the negative cable of the battery at the battery and connect a test light between the negative battery cable and the battery. If you have a draw, the light will light up. The brighter the light, the stronger the drain. Start removing and then replacing fuses one at a time from the fuse panel. If the test light goes out when you remove a fuse, you have found the circuit causing the battery drain, and you should be able to narrow down the source from there. If your vehicle does not have a fuse panel, unplug some unfused items such as the alternator or regulator and see if the light goes out.

Note:
If you are doing this by yourself you can also attach a pair of jumper leads to an old seat belt buzzer. When you connect between the ground cable and the battery it will buzz (if you have a battery drain) until you find the circuit causing the drain.