The recent brutal cold snap in many parts of the U.S. undoubtedly put a lot of strain on vehicle batteries, which lose a lot of their cold cranking capacity under such conditions. But what happens when the s battery charging system is the focal point of virtually all vehicles functions —as is the case with electric vehicles?

According to recent tests conducted by the AAA, the results were not good. AAA found that cold temperatures can reduce vehicle battery capacity by as much as 40 percent if the car heater is used. Hot temperatures also adversely affecting charging capacity, but not as much, the survey found.

With electric vehicles gaining momentum, there’s more anecdotal evidence from owners of electric vehicles, such as top-selling Tesla, that cold weather battery performance is severely hampered. Owners complained on social media about reduced range and frozen door handles during the cold snap.

For prospective electric vehicle buyers, awareness of electric vehicle limitations in cold weather is needed. “As long as drivers understand that there are limitations when operating electric vehicles in more extreme climates, they are less likely to be caught off guard by an unexpected drop in driving range,” says Greg Brannon, AAA’s director of automotive engineering, in a statement.

AAA tested several electric vehicles, including the BMW i3s, Chevrolet Bolt and Nissan Leaf from the 2018 model year, and the 2017 Tesla Model S 75D and Volkswagen e-Golf. All have a range of at least 100 miles per charge. They were tested on a dynamometer, which is like a treadmill, in a climate-controlled cell.

The automobile club tested the cars at 20 degrees and 95 degrees, comparing the range to when they were tested at 75 degrees Fahrenheit, according to a report on the study.

At 20 degrees, the average driving range fell by 12 percent when the car’s cabin heater was not used. But when the heater was turned on, the range dropped by 41 percent, AAA says.

At 95 degrees, range dropped 4 percent without use of air conditioning, and fell by 17 percent when the cabin was cooled, the study found.

AAA’s testers determined that the Tesla’s range when fully charged at 75 degrees was 239 miles, but it fell 91 miles, or 38 percent, at 20 degrees.

Tesla, for its parts, refutes many of AAA’s findings. In a statement, the company says that based on data collected from its cars on the road, “The average Model S customer doesn’t experience anywhere near that decrease in range.” The company says the range dropped by roughly 1 percent at 95 degrees, but it would not release a percentage for cold weather.

AAA says it follows test procedures drawn up by SAE, an auto engineering trade group.

Not surprisingly, short driving distances exacerbate the strain on electric vehicle batteries. Hughes notes that range takes a hit mainly for short trips, and the decrease wouldn’t be as large on longer trips once the battery and cabin are heated. Range would be reduced further by extreme cold in northern states, he says.

AAA recommends that drivers heat or cool their cars while still plugged in to a charging station. It says electric cars can still be used in extreme climates with a little extra planning.