First it was the Jaguar I-Pace. Researchers studying electric vehicle performance at Carnegie Mellon University were surprised last fall when the sporty electric crossover received a disappointing range rating from the EPA. The 234-mile rating, from a 90-kWh battery, was six miles short of what Jaguar had projected, and 16 miles short of the researchers’ own estimates. That difference might not seem like much—until you’re stranded on the side of the highway.

Now it’s an Audi crossover’s turn to disappoint. The company’s electric E-tron SUV, which goes on sale next month, just received its own EPA rating: 204 miles from its 95-kWh battery. That’s about 20 miles shy of what many had projected (though in line with a few too), a disparity that often occurs with electric vehicles because the EPA’s real-world testing can’t always be readily duplicated by researchers and manufacturers.

The E-tron’s numbers are particularly unfortunate for Audi when compared with the current electric vehicle king, Tesla, which the EPA rates up to 295 miles on its comparable Model X SUV. The car generates 74 miles per gallon equivalent, compared with the I-Pace’s 76 and the Model X’s 93.

The Audi E-tron generates 74-miles per gallon equivalent, according to the EPA's new rating. Eric Adams

As for the “why”—well, it gets complicated. Electric vehicle range has lots to do with batteries, sure, but also technology choices, vehicle weight (Audi hasn’t released the E-tron’s yet), and even engineering strategies.

For one, it appears the premium Tesla competitors’ battery systems are less efficient, and less prepared for the long haul. The Audi and Jaguar EVs deliberately use only 88 percent and 94 percent of their battery capacities, respectively. Carnegie Mellon researcher and mechanical engineer Shashank Sripad says this is probably to preserve the lithium-ion batteries’ health as they naturally degrade over time. (The stress of frequent charging can spur that degradation.)

Tesla, by comparison, appears to have better battery-engineering prowess, and more experience with the technology. “One of the possible reasons for Tesla going with the full nominal capacity could be that they have a better thermal management system, which makes sure the battery doesn't degrade as much even with full capacity,” Sripad says. Tesla CEO Elon Musk has also suggested the company has found a way to use more of its battery without compromising longevity—a sign that the electric car company is more confident in its batteries’ abilities to hold full charges without breaking down over time.