It’s shaping up to be a hot summer, taxing not just electricity grids, but electric cars too. In fact driver’s of the Chevy Volt extended range electric car are noticing reduced electric-only distances when the mercury spikes.

In a thread on GM-Volt.com owners are reporting reduced electric only range by as much as 30 percent, and in some cases even more.

“I’d been getting 43+ miles on battery since I got my Volt,” writes forum member Trakehner. “It’s been in the high 90’s, and I’m using air-conditioning and still driving the same speed…and my mileage has dropped to 32-33! I didn’t realize the air-conditioning sucks up that much power.”

Another poster, with the handle HOUSTONVOLTAGE responds with a similar problem. “Also see a big reduction in miles. At night when the temperature drops the milage goes back to normal (45 miles per charge) but during the day if its 100 degrees, I run the fan on HI in comfort mode, and get about 30.”

The issue, however, is about more than just running the A/C on high admits Michelle Bunker Malcho, of the Chevy Volt communications team at General Motors.

“Batteries are like humans when it comes to operating at peak performance in various climates — they operate best at a comfortable temperature, ” she explains. “That means that if it’s either extremely cold or hot where an EV is operating, range will be affected. This is true of any EV, not just the Volt.”

Early reviews of modern electric cars tested in the North East during the winter months showed similarly dramatic losses of range. The Volt, however, with it’s gasoline range extender, makes the electric only range less of something owners have to worry about.

Still, GM has worked to put in place preventative measures to help deal with temperature extremes says Bunker Malcho. “That’s why the Volt uses a liquid cooling/heating system that helps to minimize the range loss.” Still, she admits, “range will be affected when an EV is operated in hot or cold weather.”

That is perhaps the real reason behind the spate of complaints from owners. While temperatures in the ’90s and even rising above 100 are not unusual in states like Texas and Arizona, a recent heat wave in the Midwest and North East is causing more people to notice just how much of an effect hot days can have on an electric car.