To be honest, I wasn’t really expecting “winter” here in Northern California to have much impact on our EV. We don’t get snow, or even particularly cold temperatures. But there was a strangely noticeable impact. Up until the temperature dropped, we had been seeing economy numbers in the upper 2s and lower 3s (mpkWh). Suddenly, or it seemed that way, it was hard to even reach 2 mpkWh. Frequently, on short runs, the car would be stuck around 1.5 mpkWh. Nothing explained the loss of range, or lower efficiency.
Then, a week ago we were out for one of normal weekend errands and I noticed we were back up to almost 3 mpkWh. What changed was the temperature. Rather than being in the forties an low fifties Fahrenheit (5 to 15 Celsius) we were back into the upper sixties (~20°C).
Slightly shocked that a change of 20°F (~10°C) could have such a dramatic effect on the efficiency, I started looking for other possible causes.
One possibility was the cabin heater. Unlike an ICE vehicle, an EV lacks a hot engine that can be used to warm air for the cabin heater. Instead, they have electric heaters (usually heat pumps rather than resistive heaters, but still electric), which use some of the power from the battery, reducing the mpkWh number, and the estimated range. And if you turn on the heated seats, that adds even more drain.
Another possible cause is the battery conditioning, needed to keep the coolant in the lithium ion battery pack at an efficient temperature and the batteries warm. This seems far more likely than the cabin heater. I cannot tell if this runs all the time, or just when the car is started, but I did discover that when the temperature drops further it can be a struggle to even get 1 mpkWh on short journeys.
Over at Green Car Reports, one Chevrolet Bolt driver provides a detailed log of using his EV for a ski trip in Canada, with temperatures around -4°F (-20°C). The Bolt did surprisingly well, although something an ICE user might not expect to see was the loss of range while parked outside in freezing conditions (from the car keeping the battery safe). Compare to this, winter here in NorCal is nothing. If EVs can perform in these conditions, then most people should have no problem using one!