NEW YORK (CNNMoney) -- General Motors said Monday it will loan cars to any owner of its electric-powered Chevrolet Volt who is worried about the risk of a battery fire after a crash.
The automaker, which reasserted the overall safety of the car, had no estimates about how many loaners might be requested or how long the Volt owners will be able to use the loaner.
The National Highway Traffic Safety Administration announced Friday that it had launched a formal investigation into the risk of a fire in Volts after two Volt batteries caught on fire one to three weeks following crash tests, apparently due to damage to the battery.
A third battery began to smoke and emit sparks shortly after it was rotated 180 degrees following a crash test, the agency disclosed.
"NHTSA is not aware of any roadway crashes that have resulted in battery-related fires in Chevy Volts or other vehicles powered by lithium-ion batteries," the agency said. "However, the agency is concerned that damage to the Volt's batteries as part of three tests that are explicitly designed to replicate real-world crash scenarios have resulted in fire."
The time between the crash and the fire should reduce or eliminate the real-world risk for owners, GM executives said Monday. GM said the lithium-ion battery in the electric-powered Volt should be depowered following a crash and that, if that is done, there is no risk of fire.
Nevertheless, GM said it was making the loaner offer to reassure Volt owners while the investigation is conducted.
"Our customers' peace of mind is too important to us for there to be any concern or any worry," said Mark Reuss, president of GM North America. "This technology should inspire confidence and pride, not raise any concern or doubt."
Shares of GM (GM, Fortune 500) were up about 3% in trading Monday, although the gain came before the announcement.
The Volt is powered by an electric motor with a lithium-ion battery that is recharged by plugging it in. It also has a gasoline-powered engine that can power the car when the battery becomes depleted.
"NHTSA continues to believe that electric vehicles have incredible potential to save consumers money at the pump, help protect the environment, create jobs, and strengthen national security by reducing our dependence on oil," said the agency. It said no other electric vehicle has shown any fire risk.
The all-electric Nissan Leaf is the main rival to the Chevy Volt, although Tesla (TSLA) is also producing high-end electric vehicles. Ford Motor (F, Fortune 500) is about to come out with an electric-powered Focus.
Reuss said no Volt owner has asked for a different car since the initial reports of a post-crash fire three weeks ago.
Chevrolet started selling the Volt in January and has sold 5,329 Volts in North America through the end of October. But sales have picked up in recent months and the company said a month ago it still hopes to hit a 10,000 sales target for the year.
The Volt easily passed the the safety administration's test for protecting vehicle occupants, earning a 5-star rating for overall safety, side impact and rollover risk and four stars for frontal crash protection.
Reuss said his daughters and son all drive Volts, and he believes it is safe, despite the probe.
"We don't think there's an immediate fire risk," he said. "This is a post-crash activity. We're going to make this technology the best it can possibly be. This is safer than any internal combustion engine car." 
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