Electric vehicles have a lot going for them—they’re clean and quiet, they accelerate briskly, and they have far fewer parts than conventional gas-powered cars, reducing maintenance. But that may all be trumped by their high price tag and limited range—most go 100 miles or less on a charge. Now electric vehicles are in danger of having another black mark: several Nissan Leaf owners in hot areas of the country have been saying that the battery capacity of their cars is shrinking fast. One 2011 model could only travel 59 miles on a charge, down from the EPA’s rating of 73, and Nissan’s original claims of 100 miles. Now the results of a Nissan study of those vehicles are in. The cars are being driven too much. According to Green Car Reports, Nissan says:

Average annual mileage [of those cars] is about 16,000 per year, more than double the average Phoenix customer mileage of 7,500 miles per year.

Based on the amount of driving and the decline in battery capacity so far, Nissan expects the cars to retain 76 percent of their capacity after five years. A spokesperson from Nissan is quoted as saying that, given their heavy use, “the cars and the battery packs are behaving as we expected.”

The Nissan Leaf owners are worried that, given the rate of decline so far, the actual capacity could be far lower. (Such capacity fade isn’t covered by the battery warranty.) But even if 76 percent is accurate, that would mean that a car that’s supposed to go 73 miles on a charge will only go 55 miles—after only five years. Consumers have put up with similar capacity fade in their mobile phones—but only because they replace them so fast and don’t have to count on resale value. There’s a chance that batteries from other automakers, such as GM and Tesla, will fare better—they have better battery cooling systems (see “Are Air-Cooled Batteries Hurting Nissan Leaf Range?”).