EV Battery degradation in extreme temperatures might not be as bad as AAA says

AAA announced yesterday that electric vehicle range is significantly reduced in hot and cold weather. However, their tests are no substitute for real-world data.

It is well-known that the performance of lithium-ion batteries is affected by temperature. The AAA Automotive Research Center set out to find out the extent of these thermal effects by testing three popular electric vehicles: the Nissan Leaf, Ford Focus, and Mitsubishi iMIEV. What they found was rather unfortunate for supporters of EVs.

The test vehicles were driven on a dynamometer simulating city driving conditions in a climate-controlled room at 20 degrees, 75 degrees, and 95 degrees Fahrenheit. The average range of the vehicles was 105 miles at 75 degrees, but it dropped a shocking 57% to just 43 miles at 20 degrees and 33% to 69 miles at 95 degrees. According to Greg Brannon, the director of automotive engineering at AAA, "We expected degradation in the range of vehicles in both cold and hot climates, but we did not expect the degradation we saw."

Don’t hit the panic button just yet. It is known that cold and hot weather shorten EV range – below about 68 degrees Fahrenheit, battery life decreases linearly with temperature. Some Leaf drivers in extremely hot climates, particularly Arizona, have seen drastic drops in range due to the air-cooled battery of older and current Leaf models. Nissan is addressing this issue. However, cold and hot weather performance depend on many factors and vary in the real world. Driving style and use of heating or air conditioning significantly impact range.

Back in December, Green Car Reports published data from FleetCarma, a company that tracks data from fleet managers and private owners. They monitored more than 7,000 Nissan Leaf trips to determine real-world range and found that the average range at 25 degrees Fahrenheit was approximately 60 miles, or about a 21% drop from the ideal range of 76 miles. Even at 0 degrees the average range was still only 37% less than ideal at 48 miles. With temperatures of 95 degrees, the average Leaf range was about 56 miles, or a 26% drop from the range at ideal temperatures between 60 and 75 degrees Fahrenheit.

In short, there is no substitute for real-world data. AAA may have done the best they could to simulate actual results, but they did not release information about the use of climate control within the vehicles and used the EPA’s “stop-and-go” drive cycle, which appears to mean the UDDS cycle that represents one out of five cycles that the EPA uses to officially calculate estimated range. And as all EV drivers know, driving style affects that number significantly as do features like heated seats that use less energy than a conventional heater.

So take note of AAA’s results, and be mindful of the effect of temperature on your vehicle’s range if you own an EV. But every vehicle’s battery is different and everybody’s driving habits are different, so it would be more helpful to track your vehicle’s range yourself.

If you own an electric vehicle, what is your experience in extreme weather? Let us know in the comments section.