I'm surprised since I've never had any problems at -40C and it happened several times. I Neve had to supercharge the car under these conditions however.
Do you have a decent charger in a decent garage? If you park outdoors and have a slow charger (say 2kw) and depending on battery type - the charge might never even start as there's simply not enough heating power for battery to warm up.
I'm parked outdoors but I do have a good 40A charger, I also make sure I never get under 20% when it's that cold.