When I was traveling through Alaska and Canada I saw instances where cars would be hooked up to electric heaters to keep the oil/water/block warm enough to allow easy starting in very cold weather. How much electricity do these heaters use? How does their use compare to charging an EV?
300 to 500 W is typical for my vehicles' block heaters over the years, and my present incremental cost of electricity is about C$0.093/kW-h, so my cost of running a block heater is between C$0.03 and C$0.05/hour.
The rise in coolant temperature when heated by a block heater drops off with time - the gain is rapid at first, and drops off quickly, with 90% of the benefit occurring within 3 hours, and no additional benefit occurring after 4 hours.
Assuming one wants to run the block heater for maximum temperature increase, 4 hours will cost between C$0.012 and C$0.020.
It's false economy to not use a block heater in a cold climate; the few cents of electricity used is offset many times by reduced battery, starter, and engine wear, and greatly reduced fuel consumption.
There's also the comfort of having cabin heat much sooner, when the coolant starts at +20°C rather than -30°C.
To answer your question directly, the amount of energy used by a block heater would be miniscule compared to the energy used to recharge an electric car.