The cars included in the study were the Audi e-tron, BMW i3, Chevrolet Bolt, Ford Mustang Mach-E, Hyundai Kona, Jaguar I-Pace, Nissan Leaf, Tesla Model S, 3, X, and Y, Volkswagen e-Golf, and Volkswagen ID.4. Of the bunch, the Bolt fared the worst, its range dropping a massive 32 percent in cold weather conditions. Close behind it were the Mustang Mach-E and ID.4, whose ranges both dropped a significant 30 percent when operating at lower temperatures.
On the opposite end of the spectrum, the vehicle that suffered the least was the I-Pace, with only a 3 percent difference between its normal range and its cold-weather range. That being said, the cold-weather range was predicted by the car's onboard telematics rather than actually being tested, so there is a chance it could be slightly incorrect. That is also the case for the e-tron, i3, Bolt, Kona, and e-Golf, though the other 7 vehicles were in fact verified by Recurrent through "a combination of onboard devices and real-time usage data".
Many of the vehicles that performed the best in the study, such as the e-tron and I-Pace, were equipped with heat pumps, which can recapture heat created by the powertrain and pump it back into the cabin to keep occupants warm rather.
Why does a drop in temperature make electric vehicles less efficient? Well, it has to do with how battery performance is affected by colder climates. When temperatures plunge, chemical and physical processes within the batteries slow down significantly - reducing the EVs power output. The cold acts as an artificial barrier that impedes these reactions from taking place as quickly or efficiently they would otherwise resulting in a decrease of range when compared with warmer conditions.
Electric cars also have to make their own heat. The internal combustion engines (ICE) that power traditional cars are surprisingly inefficient. All of the energy that ICE cars don't use to propel them forward is turned into "waste heat," which is typically just lost energy. In cold weather, however, ICE cars redirect this waste heat from the engine to warm the cabin. On the other hand, an EV has a much more efficient motor which does not generate as much heat. In the cold, available motor heat is routed to warm the battery itself, meaning that cabin heating requires a power source. Cabin heaters generally draw from the high voltage battery, reducing how much battery is left for driving.
Source: Recurrent