 Battery drain
One method that I have used in the past with great success is to disconect the battery ground cable, then install a decent quality multimeter in series (set to the 10 amp scale) between the battery negative and the negative post on the battery (do not try to start) if the circuit causing the drain is active you will register a reading on the ammeter, probably a vey small reading of less than one amp if it take a couple weeks to drain the battery. Most likely it is an auxillary (add on) circuit causing the drain, simply remove one fuse at a time then check the meter, once the reading becomes zero you have found the guilty circuit. | 
