U.S. regulators are investigating the safety of batteries used to power electric vehicles after a General Motors Co Volt caught fire following a crash test.

The National Highway Traffic Safety Administration said it does not believe the Volt and other electric vehicles are at greater risk for fire than those with gasoline-powered engines, but said it has asked automakers for information on lithium-ion batteries and recommendations for minimizing fire risk.

GM and other automakers said they were confident in the technology, which is being rolled out in current electric cars and the next wave of hybrid vehicles. Toyota Motor Corp's Prius, which dominates the hybrid market, is powered by older nickel metal hydride battery technology.

The crash test for the Volt, which carries a 400-pound lithium ion battery pack, was conducted last May at a facility in Wisconsin, NHTSA said.

The fire did not break out until more than three weeks after the side-impact crash test, and the reason for the fire has not been determined, the agency said.

GM said it was not aware of any other Volt fires. A senior NHTSA official said the agency has received no consumer complaints about fires involving GM or other electric cars.

Both GM and NHTSA conducted follow-up tests and could not repeat the fire. The agency plans additional electric car battery tests with Energy Department experts in coming weeks.

``I want to make this very clear: The Volt is a safe car,'' Jim Federico, GM chief engineer for electric vehicles, said in a statement.

South Korean battery maker LG Chem Ltd, which supplies the Volt battery cells, said in a statement that is ''fully aware of the situation and is working closely with GM and NHTSA on the investigation.''

A range of new electric vehicles, including the Volt and upcoming models from Tesla Motors Inc and Fisker, are powered by the kind of batteries that have long been used in consumer electronics. Those batteries deliver the power that electric vehicles require, but the current generation of lithium-ion batteries also has a tendency to overheat.

If safety concerns were to slow the uptake of electric vehicles, that could endanger President Barack Obama's goal of putting 1 million EVs on the road by 2015. To drive that goal, the Energy Department has provided about $2.5 billion in funding to battery companies, automakers and related firms. Obama's ``green economy'' agenda is under fire from Republicans in Congress whose criticism has included some taxpayer-funded auto-related investments.

Ron Cogan, editor of Green Car Journal, said it was to be expected that electric vehicle technology would evolve and automakers would develop new safeguards just as they have with 100 years of experience with gasoline engines.

``Catastrophic things happen in crashes of vehicles with any type of fuel and obviously you have to manage those in intelligent ways as you go along,'' he said.

Clarence Ditlow of the Center for Auto Safety in Washington, an advocacy group, said the more complex the vehicle, the more likely it will be to have serious problems.

``The challenge for GM is to get on top of this as quickly as possible. The last thing they want are Volts catching on fire,'' Ditlow said.

GM and other auto companies said they have built in protections on vehicle battery packs that would keep batteries from overheating in the kind of ``thermal runaway'' event in which an overheating cell causes a fire.

``I would much rather be riding on top of a battery than a tank of gasoline,'' said Jason Forcier, vice president and general manager of battery maker A123 Systems Inc's auto business. ``It's much, much safer.''

A123's battery has a different chemistry than the Volt's that he called ``very, very safe.'' A123 makes the battery for the Fisker Karma, the BMW hybrid 3- and 5-Series cars due out next year and GM's all-electric Chevy Spark due in 2013.

'SPILLOVER' EFFECT?

Nissan Motor Co Ltd, the only major automaker with an all-electric car, the Leaf, said its battery is different, running cooler than the Volt's. Nissan acknowledged any problems with EV technology could make some consumers nervous.

``Certainly, a competitor having issues with their systems, there is always going to be some type of spillover, but our product stands on its own,'' said Bob Yakushi, director of product safety for Nissan North America.

Nissan officials said there have been no reports of Leaf fires. About 17,500 Leafs have been sold globally, including 8,000 in the United States.

American consumers have been slow to embrace electric and rechargeable vehicles, in part because of their additional cost. Pure electric vehicles like the Leaf also have limited range before recharging.

The Volt has a gas-powered 1.4-liter engine to provide additional range after it has run about 40 miles on a fully-charged battery.

GM has sold about 5,000 Volts. The plug-in hybrid costs $40,000 before a $7,500 consumer tax credit.

Separately, Duke Energy Corp has advised 125 customers to avoid using recently-installed Siemens home charging stations for electric cars until a probe of a garage fire in North Carolina is complete, spokeswoman Paige Layne said.

GM shares were off 12 cents in late trade on the New York Stock Exchange at $22.58.

Morgan Stanley analyst Adam Jonas said he did not expect any lasting impact on GM's shares, although the ``negative sentiment'' could continue for several weeks.