My bmw battery drains overnight I turn everything off change the battery twice.

Hi, I have the same problem, I worked it out to be the tail gate not closing properly. I have to slam it to ensure battry dont drain over night. Just a thought might be same with your?.

your altenator is going out

I had the same problem when I wasn't driving it enough - mainly just back and forth to work which was located only a few miles from me (this will cause countless problems for a BMW I have learned). I was also told that it could be a parasitic drain.