Probe of Chevy Volt fires closed WASHINGTON (Reuters) - The government on Friday closed its investigation of Chevy Volt battery fires, concluding that there is no defect trend and that electric cars do not pose a greater risk of fire than gasoline-powered vehicles. The National Highway Traffic Safety Administration also said that it was satisfied with a plan by General Motors to address problems that triggered fires in Volts after crash tests. "Generally all vehicles have some risk of fire in the event of a serious crash," NHTSA said in closing the two-month investigation. No real-world fires were reported by regulators or the automaker, but the investigation has cast a shadow over GM's heavily promoted bid to lead on fuel efficiency and green technology with the Volt. NHTSA opened its investigation after separate fires last year. A battery pack in a Volt crash tested in May caught fire three weeks later at a NHTSA facility. In lab tests completed in late November, a second Volt pack began to smoke and throw off sparks, while a third battery pack caught fire a week after a simulated crash. In response to the safety concerns, GM has said it will strengthen structural protection for the 400-pound lithium-ion battery in the Volt, and take other steps to prevent coolant fluid from leaking and triggering a fire. The automaker said in a statement on Friday that NHTSA's decision is consistent with the results of its own analysis Reporting By John Crawley; Editing by Gary Hill