AAA Studies Thermal Effects on EV Range

Long-range EVs? Not when the mercury plummets.


It’s been a tough winter in much of the U.S. When the Midwest hasn’t been dealing with a Polar Vortex it been smacked by a “bombogenesis.” But even normally temperate seasonal regions like San Diego, Los Angeles and Las Vegas have been hit with harsh and, in some cases, record cold this year. That’s particular bad news for the growing number of owners of battery-electric vehicles who have discovered the impact extreme temperatures can have on both range and charging times.

Percent change in combined driving range relative to testing conducted at 75°F. (AAA)

“I’m consistently seeing a 30% degradation” in range on cold days, said Henry Payne, an automotive reviewer for The Detroit News and owner of a Tesla Model 3. He’s by no means alone. “I can get 270 miles [range] no problem,” from his Chevrolet Bolt EV with a fresh and fully charged battery, said Timothy Grewe, chief engineer at General Motors’ electric propulsion lab. But Grewe notes that when temperatures fell into negative territory, “I got around 170.”

The issue of cold-weather range has been a subject of concern among BEV owners for some time, and a frequent topic on social media. But several new studies have attempted to quantify the effects. The results are significant, showing that some vehicles lose more than 50% of their range in sub-freezing temperatures, though drivers can mitigate the losses if they’re willing to limit their use of cabin heating.

AAA study

Percent change in combined MPGe relative to testing conducted at 75°F. (AAA)

One of the two recent studies also looked at the impact of high ambient temperatures and found that heat, too, can draw down range, though not to nearly the extend that cold does. Even then, degradation of range poses potentially serious problems not only for EV owners but for the automakers who are rushing dozens of new electrified offerings to market over the next few years. They’re investing tens of billions of dollars and anything that could reduce the appeal of battery-based technology could make it more difficult to recover those investments.

Percent change in combined driving range relative to testing conducted at 75°F. (AAA)

“We found that the impact of temperature on EVs is significantly more than we expected,” said Greg Brannon, AAA’s director of automotive engineering. “It’s something all automakers are going to have to deal with as they push for further EV deployment because it’s something that could surprise consumers.” The organization tested five separate models: the BMW i3, the Chevrolet Bolt EV, the Nissan Leaf, the Tesla Model S and the Volkswagen e-Golf. AAA engineers subjecting each car to both 20-degree F cold and 95-degree F heat.

The vehicles proved surprisingly similar in their response to the thermal conditions, said Brannon. He noted that, on average, they lost about 12% of their range on the cold side. That was a relatively modest decline, but it did not include the use of any form of cabin heating. When HVAC systems were activated, the range degradation averaged 41%. In other words, a BEV with an EPA-rated range of 200 miles would get only 118 miles between charges.

And those numbers don’t fully reflect potential range loss, as they don’t factor in the use of seat or steering wheel heaters or headlights during winter commutes. The impact is felt by motorists in various ways. Not only can they travel less per charge, but they also pay more. AAA estimated a typical American BEV owner would pay an extra $24.27 per 1,000 miles. The group’s study also examined what happens on extremely hot days. At 96 degrees F, range dipped 4%--if the driver was willing to sweat it out. With the HVAC turned on, range degradation climbed to 17%.

Consumers Union study

Percent change in combined MPGe relative to testing conducted at 75°F. (AAA)
Percent change in cost for 1000 miles of combined urban/highway driving relative to 75°F. (AAA)

The AAA findings were largely echoed by a separate study conducted by Consumers Union, the publisher of Consumer Reports magazine. It focused on two EVs—the Tesla Model 3 with a 310-mile EPA rating, and the 151-mile version of the Nissan Leaf. Testing was conducted at the CU track on days when the outside temperature averaged between 0 to 10 degrees F.

The Tesla used up the equivalent of 121 miles to cover 64 actual miles of driving, leaving it with a displayed range remaining of 189 miles. The Nissan fared even worse, “burning” 141 miles of stated range to travel those 64 miles. At the end of the test, the second-generation Leaf had only 10 miles showing on its range display.

Electric habitable zone

Part of the problem, said the AAA’s Brannon, is that “lithium-ion batteries like the same sort of temperatures that we do, around 70 degrees.” Much below that and the chemistry used to store energy runs into various problems. Among other things, battery components develop increased resistance that limits how much power they can hold, as well as how fast a battery pack can be charged or discharged, explained GM’s Grewe.

A decidedly unscientific test of a Hyundai Kona on a 20-degree F day in Detroit found it was only able to go from 31 to 110 displayed miles after being plugged in for 45-minutes to a 50-kW SAE Level 3 charger. That’s barely half what the automaker normally promises under ideal conditions.

Of the five brands included in the AAA range study, only Tesla raised any real concerns with the results. “Based on real-world data from our fleet,” said a spokesperson, “the average Model S customer doesn’t experience anywhere near that decrease in range at 20 degrees Fahrenheit, and the decrease in range at 95 degrees Fahrenheit is roughly 1%.” That said, Carl Phillips, a Nissan executive working on the Leaf program, said there is no question, “temperature has an impact” on range, adding that “all EVs perform similarly in cold weather.”

There are some ways that an owner can reduce range degradation, according to industry experts. Most battery-electric vehicles can be “pre-conditioned” when they are plugged into a charger. That means a motorist can use a smartphone app or software built into the infotainment system to start warming the vehicle’s cabin up before they leave home, office or store, using grid energy. Automakers also encourage drivers to reduce their winter reliance on the HVAC system and stay warm using seat and steering wheel.

AAA methodology

AAA conducted primary research in partnership with the Automotive Club of Southern California’s Automotive Research Center (ARC) in Los Angeles to understand impacts of ambient temperature on electric vehicle driving range with and without the use of the HVAC system. Testing was conducted using the following equipment: ampere-hour meter, OBD-II scan tool and dynamometer.

Test vehicles were selected using a pre-determined set of criteria such as availability for sale throughout the United States with a minimum EPA estimated driving range of 100 miles. One vehicle per manufacturer was tested to prevent over representation of a single brand. Additional information on methodology can be found in the full report .