Electric cars do tend to perform less well in cold weather due to the effect of temperature on battery efficiency. However, mild hybrids have small batteries compared to EVs, and are commonly fitted with nickel metal hydride batteries which are less affected by cold weather compared to lithium ion batteries in EVs. Also the mild hybrid system contributes a small percentage to how the vehicle operates compared to an EV which is solely reliant on the battery. EVs, hybrids, petrol and diesel cars all perform less well in cold weather, so we would expect a decrease in efficiency for all vehicles when the temperature falls.