I just got the car back. and this is what seems to be the issue.
A diagnostic test revealed that all faults pointed to the battery being low and running at around 70%. Nothing else was found. They charged the battery overnight and it is now at a 100%.
Now for the reasons: Most likely, when I got the car, just before Christmas, the battery was already low, but not to the point that it would trigger an alarm. With the recent cold spell, it worsen the issue, although in my case, I started getting the warning when it was still mild. So not sure really.
The tech told me that because of all the electronics, some of which according to him stay on long after the car is shut down, in cold weather, the battery depletes. Although I understand the concept, I find troubling that this is happening. I mean, this is not my first winter but getting this with a brand new battery, is troubling. Although I suspect that because there is a warning, you are informed, where some other cars can have the same and you just wouldn't know until you can start the car.
The good thing is that they told me that if it happened again, they would most likely end up changing the battery since the remainder of the charging system checks OK.
So we will see.
2016 F26 Alpine White M40i
2014 F25 Alpine White 35i Sport - Retired
2012 F30 Melbourne Red 335i Sport Line - Retired
2007 E92 Space Grey - Retired