My 540i seems to have difficulty holding a charge. I use it mostly on weekends, so it can sit in a cold garage during the cold months for five days at a time.

On a cold day, it wouldn't start. The door locks and interior lights worked and I could hear the click of the solenoid (?), but there wasn’t enough power for it to turn over. I charged the battery with an electrical charger.


After a full electric charge, I drove it for about 20 minutes, parked, and came back in about half an hour. It started and I drove another few minutes and parked again for about half an hour. This time the car wouldn’t start. I got jump start from another driver, and it turned over right away.


While driving the car, the alternator light does not come on and everything seems to be running okay, including the heat. Do I just need to give it more of a charge? Could the battery not be charging while the car is running from a problem other than the alternator?