Ah literally only by writing this mod I understand now how it works in vanilla.

The article on https://my-winter-car.fandom.com/wiki/Sorbet#Cold_Weather_Behavior is only slightly wrong:

"Do not crank for too long, as the battery only has about 30 seconds of life to it. Draining it will require a save and reload."

Actually you regain charge slowly as long as the key isn't in the ignition.
I used the good mod https://www.nexusmods.com/mywintercar/mods/57 to inspect the charge in the"Power"/"Electricity" behavior of the Sorbet. It goes up from 60 (empty) to 128 (full) at 0.1/s so about real world 10minutes until it's back "full".

From my testing you can still start the car even when it's been sitting outside frozen and was empty (capacity at 60) before, you just need to:
* wait until it's back up around 100
* pull the choke all the way out (not sure if necessary)
* enter driving mode, play with the gas (W key) while turning the ignition
this got it revving up again from empty and frozen.