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.

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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.

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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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