Same thing happen to mine after being park outside at the airport the last two week in these sub-zero temperatures. After the 45 minute drive home and sitting in my garage overnight out of the wind, it was fine the next day.
"BMW
Increased Battery Discharge. BMW cars equipped with the intelligent charging system may display a warning message stating Increased Battery Discharge or High Battery Discharge. This problem often happens when you first start your BMW in the morning, especially during extremely cold weather."
