BMW 330ci Chronic Dead Battery

I have a 2006 BMW 330ci. I purchased it in Feb 2008 with a clean maintenance record. I’ve only put 2000 miles on it since Feb 2008. For the second time since I purchased the car, I left it sitting for 2 weeks without starting it and it completely died. Not even my key remote worked!!! The first time it happened the dealer replaced the battery and said the car was otherwise fine (checked alternater, etc). The second time they put in a larger battery (yellow top) and are telling me I need to start the car every now and then(which gets complicated when you fly around the country for a living) or hook it up to a trickle charger. They are telling me that even when the car is off it’s electrical components are checking on each other (13x an hour) and draining the battery. I can’t believe this is normal and that every BMW in the world has to be started once a week to not drain the battery dry. So my question is do I need a car sitter when I leave town? Should I have bought American? Or is there some other thing going on?