My other car is stored in a garage without power and the battery depletes after about six days due to the alarm/immobiliser.
Now I detach the negative battery connector upon parking and reconnect the battery when I pick it up and the alarm/immobiliser kicks in and the battery is fresh as a daisy - I could leave it weeks.
Works a treat - would have to work a bit harder to get to it on the mog but better then it going flat.
You know it makes sense! 
