Do take the time to hook up a charger to the batterry at least to test it. (I know you have to take out some interior trunk trim and it's a PITA, but give it a try).
I am new to BMW, but I had a new batterry, and we drive it basically relatively short distances (insufficient to keep battery charged). I did not have the exact symptoms you've encounter (08 528 XI) but I did have clocks going out, lights out, and warnings as to 4wheel/dsc malfunctions. A recharge solved it all.
I'm guessing only, but I think all the electric options exceed the batterrys capability, and the computer system shuts down certain electric functions when battery capacity is low.
I bought a $70 Shumacher charger (at any big box), pigtailed some charging cable directly to the battery so I can plug it in easily. and charge it every several weeks. No more problems related to electrically controlled functions.
Hope it may work for you