How efficiency is measured
An EV's efficiency is the energy it uses per distance. US labels show kWh per 100 miles, where lower is better, and MPGe, where higher is better. MPGe treats 33.7 kilowatt-hours of electricity as equal to the energy in one gallon of gasoline. Many drivers prefer miles per kWh, which works like MPG: divide 100 by the kWh/100 mi figure to get it.
Range is battery energy multiplied by efficiency. A car that can use 60 kWh of its battery at 3.5 miles per kWh can go about 210 miles. Change either number and the range changes with it. Those figures are an example, not a particular car.
What works differently from gas cars
- City driving is efficient. Regenerative braking turns the motor into a generator when you slow down, putting some energy back in the battery. Stop-and-go traffic costs an EV much less than it costs a gas car.
- Highway speed costs more than you'd expect. Electric motors are efficient at all speeds, so air drag dominates on the highway. Many EVs get noticeably less range at sustained high speeds than in mixed driving.
- Idling costs very little. A parked EV uses energy only for the cabin, the electronics and battery temperature control.
Cold weather
Cold is the biggest range factor most EV drivers notice. A cold battery delivers and accepts energy less readily, and heating the cabin uses power that a gas car gets free from engine heat. US government testing has found that freezing weather can cut range by a third or more on short trips with the heater on. Ways to soften the hit:
- Precondition while plugged in. Many EVs can warm the cabin and battery from the charger before you leave, so the battery stays full.
- Use seat and steering wheel heaters. Heating you directly uses less energy than heating all the air in the cabin.
- Park in a garage when you can, so the battery starts warmer.
- Expect slower fast charging on a cold battery, and plan a little extra time on winter trips.
Heat affects range too, mainly through air conditioning and battery cooling, though usually less than deep cold.
Charging and battery care in general
Battery makers design packs to last many years, and capacity declines slowly with age and use. Many vehicle makers suggest charging to less than full for daily driving and saving full charges for long trips, and avoiding leaving the car at a very high or very low charge for long periods. Recommendations differ by vehicle and battery type, so follow the owner's manual for your car.
The range estimate on the dash
The range display is a prediction based on recent driving and conditions. After a run of highway driving in winter it will show less, and after gentle city driving it will show more. Treat it as a guide and leave a margin, especially in cold weather or when chargers are far apart.
Habits that help any EV
- Drive smoothly and use the car's regenerative braking settings as the manual describes.
- Keep highway speeds moderate on long trips.
- Keep tires at the placard pressure. See tire pressure.
- Remove roof boxes and racks when you don't need them.
EV range FAQ
Do hybrids work like EVs?
Partly. Hybrids also recover braking energy and do well in city driving, but they run on gasoline and their mileage follows most of the same rules as a gas car. Plug-in hybrids add a short electric range on top.
Where can I compare official efficiency ratings?
The US government fuel economy website, fueleconomy.gov, lists EPA ratings for electric, hybrid and gas vehicles, including kWh/100 mi and estimated range.