I went on a trip for 6 days the x5 just sat, came back and the car wasn't significantly discharged.

The next day drove it 3 miles to work and drove home, I could see the alternator charging at 14+ volts and holding battery with 13.8. All looking good!

The following day I drive to work and see it holding with alternator putting out ~13.8. Then I go to lunch and see it showing 11.9 volts so no charging is taking place. why? after work I drive home still no charging with 11.9 volts. I hook up the 10 amp battery charger and see the battery is about 50%? discharged. Over hours I charge the battery up. Then when I use the x5 it is once again charging and holding with 13.8+

I believe there is a drain which takes battery down, seems like when the battery gets lower than 25%? down then voltage regulator refuses to charge the battery?

What do you all think?

I have a valeo regulator and brushes I ordered on ebay, I am now wondering it is time to pull the alternator and try replacing the regulator. I would bet a BMW engineer somewhere would know these symptoms, wish I knew him!