Dont know if any of you guys have considered this.... I was having the same problem and getting a high battery drain message first thing in the morning. I have my cell phone connected thru Bluetooth to the car.... When I park my car in the garage at home and dont lock the doors or dont press the start button a second time to deactivate the 'radio readiness thing' my cell phone still maintains an active bluetooth connection to the car from within my bedroom at home. I think after about 15-20 mins the car shuts off all the power to the bluetooth and other controls within the car and powers down... but I think that sustained connection for 15-20 minutes is draining the battery somewhat. The next day I get the high battery drainage message but the car recharges with that morning drive. I experimented with this a little bit and seems to hold true. When I press the start button a second time to shut off the 'radio readiness' and power down the bluetooth connection (or lock the doors which does the same), I dont get that high battery drain message and vice versa. Could this be a factor in your guys' message? Hope it helps.
KD