I am new to the BMW world, but have just purchased a 2002 520i. Great car, but I have not been able to solve a small problem - I can't keep addresses saved to the gps address book. Addresses appear to save initially and can be viewed, but after the car is turned off for more than a few minutes the address dissappear from the memory and need to be re-entered. Is it possible that there is an internal battery that has gone bad and needs to be replaced? Has anyone had a similar problem?