i've been having the exact same problem for the past few months... took several trips to the dealer, first they switched out the battery, then the second time they said it was a problem in the gauge cluster and replaced it, and after that didn't work they replaced the ipod module convinced thats where the draw was coming from. but low and behold, i didn't drive the car this past weekend and monday morning i had to get a jump to get to work.
needless to say, its been quite frustrating.
please post if you find the source of the problem.