X-5 Battery Drain

[JAndersonX5]

I have a 2005 X-5, which has had a chronic problem with the battery discharging while parked in the parking garage where I keep it in NYC. I have had it to the dealer 3 times for this problem. They found a problem twice according to their diagnostics, and the third time replaced a part that they said was one of three potential, historical X-5 causes of battery drain (even though they found no actual problem this time). In other words, they have been EXTREMELY responsive in trying to correct the problem. After the third fix, I drove the SAV from NYC to Key West (with a trailer that it towed like a dream, BTW), and it ran PERFECTLY for months. I am now back in NYC, and after 4 days in the parking garage, the battery was STONE dead again!

I have to believe at this point that they are doing something in the garage. The guys are conscientous, so I don't think they are sitting in it and listening to the stereo... Is there anything that might cause this discharge in the way they park it? Would leaving the valet key in the ignition keep some computer system from going to sleep? Has anyone else encountered this problem?

General notes:
- The garage is underground, and never really gets below 60 degrees, so it's not too cold
- The vehicle in not equipped w/ stability control (not trying to level itself while parked)
- They keep the windows down, and keep the car unlocked (could that somehow affect security features?)

HELP!!!