Electric cars in cold weather

Why winter costs range

• Heating the cabin. A petrol car heats the cabin with waste heat it makes anyway. An electric car has almost none, so heat comes from the battery. A resistive heater draws 3 to 6 kW, which at highway speed is a tenth of what the motor uses.
• The battery itself. A cold battery holds its charge but gives it up less willingly, and the car spends energy warming it before it will charge fast.
• Everything else. Dense cold air, winter tyres, wet or snowy roads and more time in traffic with the heater on.

How much

Around freezing, expect 15 to 25% off your car's mild weather range; at minus 15 or below, 30% or more. Short trips are hit hardest, because heating the cabin and battery from cold is most of the energy used on a 10 km drive. On a long drive, once everything is warm, the loss is smaller. A 400 km car is a 300 km car in a Canadian January, which is still a stop every two and a half hours.

Heat pumps and preconditioning

A heat pump moves heat from outside into the cabin rather than making it, and uses a third of the power of a resistive heater in mild cold. It cuts the winter range loss by a third or so. It is standard on many cars and an option on others, and in a cold climate it is the option to tick. The car pages say which cars have one where the data does.

Preconditioning is the car warming its battery before a charge. Most cars do it on the way to a fast charger when you navigate to one in the car's own maps, and some let you start it by hand. A warm battery charges at its normal curve; a cold one can charge at half speed for the first ten minutes or more. Set the charger as the destination in the car half an hour out.

Charging in the cold

• Precondition, or arrive after an hour of driving, which warms the battery anyway.
• Expect the first minutes to be slow and the stop to be a little longer than the planner's estimate, which is for a warm battery.
• Charging at home overnight is unaffected; the battery warms itself as it charges. Plugging in while the car is still warm from driving helps.
• Cables stiffen and connectors can freeze. Keep a glove in the door pocket.

Winter habits

• Preheat the cabin while the car is still plugged in, so the warmth comes from the wall, not the battery.
• Use the heated seats and steering wheel more and the cabin heat less. They warm you for a fraction of the power.
• Park in a garage if you have one; a car that starts at plus 5 rather than minus 10 has most of its range back.
• Keep the battery above 20% in a hard freeze, so there is always enough to warm itself and you.
• Fit winter tyres where winters call for them. They cost a little range and give back the car.