Good to know: BMW does not charge battery fully - in order to facilitate re-gen engine braking.
I.e. battery is not fully charged - which is bad for life - both in cold and heat. A lot of people on X3/X4 sites use trickle chargers - preferrably CTEK (Made in Sweden
) I "fill up" my battery at least once a month - preferrably when car parked for some time - I have two, and a garage.