Hi all, first post!
Any thoughts on an issue with my 2006 535d touring; have only had the car a month or two and find the clock and date keep resetting - so annoying! I read that this is usually a warning sign of a failing battery, so I bought a (high-end) charger (cheaper than a new battery!) and charged it up - clock re-set two days later. Then I had the battery checked at Kwik Fit; it came out 83% charged (which is pretty good?), but re-charge still recommended (only 5 days after a full charge). Altenator was also fine. I had the battery replaced yesterday just to be on the safe side (I do quite a lot of short journeys, and winter is coming!) with a fairly high-end unit from Kwik Fit (black AGM 100aH), and hey presto, clock and date reset this morning! Annoying! Once it also re-set the clock after a very long motorway run the night before.
The new battery has not been coded/registered to the car, which I may get done (BMW want £140 for this - outrageous!), but it can't be purely a coding issue as I had exactly the same problem with the original battery which was OEM factory fit. I have read about many others having similar problems, but most of them seem to resolve with a new battery. I have also read it could be the Intelligent Battery Sensor? Or something else? Any thoughts or advice much appreciated.