yukonleaf wrote:Thanks so much for your replies Nubo and Alozzy!!
I don't have leafspy BUT - car is starting to take a charge - I am using the trickle charger to be extra careful. Significant weight off my chest. Time for a glass of wine... I have had the car for 3 winters now with no problem having it sit overnight at very low temps as long as it is plugged in. Seems the battery warmers are enough to keep the battery from getting too cold. But no external power supply for a week is of course deadly. I think the car was charged when the cold spell started so there was a lot of battery left to run the battery heaters, that was probably a good thing...
LiON batteries do not like being charged quickly at extremely low temps (<0 F). I've read that an irreversible metal plating reaction can occur, resulting in permanent capacity loss. At extreme temperatures, the car will refuse to charge or only charge at 500 to 1000 W, even when connected to a 40 amp 240 V EVSE. It sounds like you found those temperatures. Good luck, it sounds like you didn't freeze the electrolyte (it's organic, not water, but can still freeze) or burst any cells, so you got lucky this time.
When it gets cold here (0 to 20 F), I specifically use up extra charge during the day (blasting the heater, driving inefficiently, taking extra trips, etc.) so that I can keep charging the battery all night on L1. This helps keep the battery "slightly" warmer. One day last winter I had 0 F and zero temperature bars showing on the dash for my 4 mi trip home. I drove a few extra miles and arrived at LBW (maybe 20 total that day, with the heat blasting 5 KW the entire time). I have a 2011 without the winter package that included the battery heater. In your environment, I would invest in heating pads under that battery (search MNL for a guy that did that in eastern Canada), a tarp, parking in an insulated garage, etc.