so for anyone wanting to know, it did resolve the issue for me aswell

tnx

 

Thanks for this thread. I can confirm the voltage regulator is the problem. My car is e90, for months, the voltage was low upon startup. Using a usb charger with a voltage reader (which is same as voltage seen through the hidden button function at odometer) car voltage was always low around 12.3v going down to 11.8v and even lower on cold days. On hot days it takes 20 minutes of driving for the alternator to charge up. On colder rainy days, it takes 50 minutes of driving for the alternator to kick in showing 13.8v, 14.1v. On unlucky rainy nights, the voltage keep on dropping down to 10v and lower 9v when then all sorts of lights errors turn up on the meter. It seems the alternator likes hot engine room and i confirmed this by driving harder, higher rpm lower gear for first 15 minutes upon startup. But it does not make sense. So,
1. Changed the carbon brush only. Problem persisted.
2. 3 minths later, changed carbon brush again but at professional shop. Problem persisted.
3. Having read this forum, changed the voltage regulator completely. Problem solved. This took 4 months before arriving at a good fix. Thanks.
Hope this thread will benefit others with similar problem. My car is 2005, e90 320d, 220k mileage.