I have had my 2002 X5 for nearly two years now. When it arrived from purchasing it second hand from interstate I had problems of the battery loosing charge randomly. - It was winter at this time. After about a month the problem disappeared. I have experienced the problem once more 12 months later.
I did notice once when I first got the car and was trying to work out what was going on with the battery goin dead that the TV screen came up with BMW on it - they keys had not been in the ignition for about 30 minutes.
The above issues / solution sounds like it could be correct. Everyone said I needed a new battery. I certainly didn't