Sales of electrified vehicles in the United States have slowed dramatically in the last year, causing concern that the emerging technology has lost its charge.

A study by online automotive research company Edmunds.com suggests a stall in the market for electrically powered cars, led by a decline in hybrids.

“This was a market that was supposed to grow, relatively rapidly, as people embraced these new technologies and more brands began selling these models,” said Edmunds senior analyst Jessica Caldwell. “That hasn’t happened.”

Caldwell’s research showed substantial gains in the pure EV and plug-in hybrid segments – 35 percent and 44 percent, respectively.

But the study also showed a drop in traditional hybrids – by far the largest segment in the electrified vehicle market – that offset sales gains in pure EV and plug-in hybrids sales, which remain a tiny fraction of the market.

“The EVs and plug-ins have shown growth,” Caldwell said, “but it’s like a rounding error in the whole electric drive vehicle market.”

The slowdown in traditional hybrid sales comes despite the success of the Toyota Prius – the best-selling car in California last year – and manufacturers’ continuing efforts to introduce more hybrid models.

Further, it comes during a year in which sales of all cars have been booming. The industry just reported its best August in more than a decade, and it has gained about 5 percent so far this year compared with the same period last year.