This is a very interesting post. I have an E53 X5 and have the same sort of problems (occasional reseting of the date and time, etc.) which I am told are most likely due to battery discharge. In any case, I am amazed that BMW did not solve this problem sooner. Here is what I think they should have done/do: BMW currently sells a solar panel battery charger that consists of a placemat size solar panel with a cable that plugs into a cigarette lighter socket that slowly maintains battery charge (provided the car is out in the sun). My suggestion would be to make the entire sunroof (or panorama roof) have this solar panel and as long as the car is stationary and in the sun the battery would be fully charged. Anyway, just a thought.