I cannot count how many theories have gone back and forth about what might be behind this charging problem. Several have been ruled out. I don't remember who first mentioned the cold, but I do have some evidence on that. The first time I remember having trouble charging was Sept 25, which was also the first day that the ambient temperature was below 60 degrees when I got home. (See, those tedious trip logs do come in handy.)
It was also the first time I ran the battery way below 0% to see what would happen. (That is how I remember the date, I posted a blog entry about it here.)
The only things I can say with confidence is that if battery charge is low on a cold day, I have trouble charging at 240 volts from the wall box in my garage. Pretty much every other theory I have examined seems to be full of holes.
The last couple days were about as cold as I have recorded this season, with low twenties yesterday. I was driving loaner Mini E # 008 until this morning, and I had more trouble getting #008 to charge than I ever had with my #458. This morning when I got #458 back from Princeton Mini, I had just as much trouble as with #008. The common element is temperature around freezing.
And both cars charge fine at 120 volts.
So when the engineers from Mini make a house call, we need to pick a cold day and I need to run the charge down low on the car. Heck, they can bring #008 by again if they run the charge down, then we have two chances to figure out the problem. Because once the car starts charging at 240 volts, the problem disappears until the next drive cycle. And you can fix the problem if you cannot reproduce it.