I have a 2000 M5 and while I haven't had the types of problems that you have, I do know that BMW knows of a voltage drop when you first start the car. For me it exhibits itself a couple of ways. Sometimes I get the flat screen with the line and nothing else showing but more often I get the Radio/Nav screen coming up to the Menu screen not the radio screen where I left it. It also takes a few seconds for the radio to turn on.