That's partly because the battery must supply some of its power to heat the cabin, and partly to more sluggish chemical reactions inside the battery itself. Plus, the battery will be tapped for heat to warm itself up to its optimal operating range, further lessening driving range.
Now, Tesla is working on a feature that will allow owners to preheat the vehicle battery from the mobile app while the car is still plugged in. Electrek reports the feature is part of the recently released 2017.50 vehicle software update and a forthcoming mobile app update.
Tesla already allows customers to pre-heat the cabin of their vehicles through its mobile app, as do automakers like BMW, through its i models, and Chevrolet with the Volt, and some others, all while the cars are plugged in. Tesla also has begun displaying the portion of driving range that is lost when the battery is cold, Electrek says. The new capability is expected to restore much of that lost efficiency — again, provided the vehicle is plugged in.
FleetCarma in 2014 found that heating the cabin and battery of a Nissan Leaf can increase the auxiliary power load from below 1 kilowatt to nearly 3 kilowatts as the mercury plunges from 68 degree F to 10 degrees. It found that the best range for EV batteries is between 60 and 75 degrees F.
Of course, plenty of people drive EVs in cold-weather climates — hello, Norway — and decreased efficiency becomes less of an issue as battery technology improves and driving ranges push past 200 miles for electric cars like the Chevy Bolt and Tesla Model 3. FleetCarma also recommends EV drivers use the time their vehicle is plugged in to preheat the cabin and battery as one of several tips for maximizing efficiency of EVs in winter.