Hi, you could try and take the positive lead of the battery at night, and then replace it the following morning if you battery is still charged then you know the problem is else where, on my horsebox i had an isolator which was on the positive side of the battery i cut into the main wire and conected it to the isolator then the wire joins back to the main feed wire, this also works well as a immobilizer. as long as you remember to turn it off and take the key out. hope this might help.
james
February 2009