Let's keep posting about these battery issues here in Canada.
My colleague with a new X3 asked me whether I have the same battery discharge warning light that he keeps getting: yes.
Dealer looked at the fault codes on my F31, reset them, charged the battery and everything was OK.
I drove home and parked in my heated garage, left my car over the weekend and on Monday am when I drove it 10 minutes to work in -25C I got the warning light again! Strangely it went away when I filled up with gas.
Anyhow, it must be that these batteries, the alternator are crap or the power management module or whatever needs to be replaced.
Wish me luck parking in Jasper NP over 3 days this weekend in -30C temps. I hope I can start my vehicle at the trailhead...