Heat wave lowers driving range in some EVs by 31%

Recent extreme heat across much of the Southern and Western U.S. is highlighting a problem with electric vehicles — their range wilts as the temperature climbs into the stratosphere.

Recurrent, a Seattle EV battery and range analytics company, tested thousands of vehicles in a variety of weather conditions.

Many vehicles experienced significant declines in range as temperatures rose, and some suffered a 31 percent plunge when temperatures reached 100-plus degrees Fahrenheit. At cooler temperatures, the tested vehicles' range loss was not as high, with an average of 5 percent reduction at 90 degrees and 2.8 percent at 80 degrees.

In calculating these average temperatures, Recurrent used a blend of data from the 17,000 vehicles the firm tracks. The data includes 65 models of EVs and plug-in hybrids. They included Tesla Models 3, Y, S and X; the Chevrolet Bolt EV; Hyundai Kona; Nissan Leaf; and Ford F-150 Lightning and Mustang Mach-E.

Recurrent did not release the names of the poorest performing models. Tesla's cars had the smallest range degradation in heat but also had the widest gap between their real-world range and the EPA's estimates.

Recurrent CEO Scott Case said the Tesla model's resistance to range declines caused by extreme heat are most likely a result of the use of heat pumps instead of standard automotive air conditioning systems.

"Heat pumps are so much more efficient at cooling," Case said.

Tesla models' heat pumps handle both heating in the winter and cooling in the summer. There is also what the automaker calls "cabin overheat protection" that can prevent its cars from getting too hot to begin with, Recurrent said.

Recurrent is working to gather more detailed data for what extreme heat does to an EV's range, but Case said that's tricky because so much driving is done early in the day, when temperatures are not as high.

Dallas, for example, had a peak temperature of 106 degrees on July 18, "but it didn't break the mid-90s until noon, so that means any driving data we have from a morning like that wouldn't contribute to our 100 degree-plus data set," Case said.

While Teslas escape big range declines during the hottest days, Recurrent's testing found that under normal operating conditions, they averaged about 60 percent of their estimated EPA range, which is 358 miles for a 2023 Long Range Model 3.

This latest heat wave has shown that Teslas aren't immune to extreme temperatures. Carlos Nossa, a scientist who commutes multiple times a week in a 2022 Model 3 between Bellaire, Texas, a Houston suburb, and Austin, Texas, has seen hot weather eat into a Tesla's range.

"I noticed that the car was using the battery quicker," Nossa said.

Before the heat wave, his Tesla had 40 to 50 miles of range left when he would arrive at his Bellaire home.

During his last two trips back to Bellaire, Nossa noticed his Tesla had 10 miles left and decided to play it safe by partially charging his car at a station outside of Austin.

That added 15 to 20 minutes to his three-hour commute, Nossa said. But he would rather add that time than get stuck in rural Texas where there are few charging stations.

"I kept calculating maybe I make it home, and there's still 10 or 11 miles left, but if it goes faster than that, I'm screwed," Nossa said.

The range decline from extreme heat has its roots in battery chemistry, said Greg Less, technical director of the University of Michigan Battery Lab.

"Once you're above [104 degrees Fahrenheit] you start to have a breakdown of the passive emission layer on the anode, and that breakdown will then cause consumption of the liquid electrolyte, which will shorten the lifetime of your battery," Less said.

However, Less doesn't think the heat will damage EV batteries because the cars aren't always driving in 104-degree weather, and EVs have systems to cool batteries.

"All electric vehicles have a cooling system on their battery pack, and that cooling system might be pumped liquid; it's probably some sort of passive cooling liquid, plus airflow," Less said. "It requires electricity; that's going to reduce the amount of electricity available to propel your car down the road."

An EV's increased electricity use in high temperatures has more impact on its battery range than direct heat, Less said.

"You're running the fan harder, you're running the refrigerant faster," Less said. "All of these things take more electricity. So that's going to reduce the range."