Level 2 charging (i.e. 240V home charging) is not affected by cold temperatures unless it's well below freezing, like below 0 F.
> In Oslo it hasn't dropped below -20C / -4F since 2010.
-20C is brutally cold, far colder than any coldest winter day I ever experienced while living in the northeast USA.
Aside from the general post-communism, we had -30C cold snaps.
But yeah, snot freezes at around -18C - I consider this the point at which things become universally unpleasant regardless how prepared you are.
That being said during a cold snap of -22C I saw my neighbours struggle to start their ICE cars while my hybrid just brutally kicked the engine into action.
The only car temperature problem I've had in the winter in Virginia hasn't been with an EV at all - just a VW diesel that had trouble starting due to extreme cold.
4 miles/hour is very, very slow. It's the maximum output of a standard wall charger. Maybe you were at a level 1 charger?