This is super common and nothing to worry about.
BMWs' battery monitoring systems are SUPER sensitive and these type of warnings have been present since the EXX chassis especially during winter times.
Like mentioned above, I also plug my car into battery maintainer as it is not being driven much these days but it would not be uncommon to get a warning after it sits for a couple of days of not being driven.
I never had a dead battery or any other problems besides the warning itself.......and yes, my car has cameras installed and draws much more power in comparison and still no problems
