GM has started to contact Volt owners, offering free loaner cars while federal regulators investigate reports of fires associated with damage to the battery in a crash.

The National Highway Traffic Safety Administration started to look into lithium-ion batteries used in electric and hybrid vehicles after a Chevy Volt caught fire in a storage facility this summer, after it went through a side-impact crash test. The crash text damaged the Volt’s battery and ruptured the coolant line, resulting in an electrical fire even after a significant amount of time had passed.

The NHTSA announced that they are launching a formal defect investigation into Chevy Volt batteries.

“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,” an NHTSA release 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. NHTSA is therefore opening a safety defect investigation of Chevy Volts, which could experience a battery-related fire following a crash. Chevy Volt owners whose vehicles have not been in a serious crash do not have reason for concern.”

Here’s the official statement from the NHTSA on the Volt battery fire issue.