First of all, join BMWCCA.
This is your local chapter of BMWCCA; if you look at link, they have 3 recommended garages in your area.
https://peachtreebmwcca.org/
Buy a Battery Tender, CTEK or Schumacher battery "maintainer" and use it when car not used for over a week. Simply hook it up for over night.
85% of all electrical issues are caused by lose or dirty connections and are often difficult to find. The BMW indy garages know where to look for problems but also people themselves have solved their problem by simply disconnecting all battery connections [in trunk, under hood], cleaning the terminals and reattaching.
My battery in my 128 is still the original one; car is a 2008. I know its weak [car is stored every winter on Deltran] and soon will have to get a new one but I have never had a problem with it.