DETROIT (WWJ/AP) – Federal officials are investigating the safety of lithium-ion batteries in General Motors’ Chevrolet Volt after a second battery fire following crash-testing of the electric car.

The National Highway Traffic Safety Administration says three Volt battery packs were crash-tested last week. In one instance, the battery caught fire afterward, and in another the battery emitted smoke and sparks.

NHTSA says it has opened up a formal safety defect investigation of those batteries.

Last May, a fire erupted in the battery of a Chevy Volt that had been damaged during a government crash test three weeks earlier.

GM continues to stress the Volt is safe and has said that the government did not follow the car maker’s protocol for storing post crash batteries.

Read more from the NHTSA.

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