* No battery fires in three IIHS crash tests this year
* IIHS 'top safety pick' promoted by GM
* NHTSA also has no plan to change its "five star" rating
By John Crawley
WASHINGTON, Dec 5 (Reuters) - An influential insurance group has no plans to strip the Chevrolet Volt of its top crash safety rating or retest the vehicle, bolstering General Motors' position that its electric car is safe despite a probe of battery fires by federal regulators.
While the Volt represents less than 1 percent of GM's U.S. sales, the plug-in hybrid has been the centerpiece of the top U.S. automaker's attempt to rebrand itself as a leader in green-car technology and fuel efficiency.
The 2011 GM Volt received five stars for safety in Insurance Institute for Highway Safety testing last February.
The ratings from the group, which is underwritten by insurance companies, are closely watched by consumers and are often used in automakers' marketing.
The safety group found no evidence of damage to the Volt's battery packs in its tests.
"If we had found that the battery pack had been damaged or certainly if we had subsequent concerns about fire risk - that would have raised red flags," IIHS spokesman Russ Rader told Reuters.
Rader said IIHS would not repeat tests in this case because its role "is not to investigate potential defects."
The National Highway Traffic Safety Administration opened an investigation on Nov. 25 into the safety of the Volt's battery pack after its own repeated tests uncovered fire risks.
A lithium-ion battery pack in a Volt that had been through a NHTSA crash test in May caught fire three weeks later at a test facility in Wisconsin.
In other battery tests completed Nov 18 by NHTSA, a second Volt pack began to smoke and throw off sparks. A third battery also tested by NHTSA caught fire as well.
NHTSA also has no plans to change the Volt's "five-star" safety rating, another key resource for consumers.
But Joan Claybrook, a former NHTSA administrator and long-time safety advocate, said the problem is now known and IIHS should do more work.
"They have a duty to inform people when they've rated a vehicle as 'top rated' and make it clear there's a problem," Claybrook said.
IIHS assesses driver and passenger protection in front, rear, side impact crashes and roof strength.
GM noted the IIHS "top safety pick" designation in its letter to Volt owners last week that explained circumstances behind two battery fires and offering them a loaner car.
It has since offered to buy back Volts. GM sold more than 6,100 this year through November.
GM previously noted the Volt battery pack, which weighs 400 pounds, gives the small car additional mass that provided an edge in IIHS testing of passenger protection.
Although it is in its early stages, the NHTSA probe could eventually lead to a recall. GM CEO Dan Akerson told Reuters in an interview on Thursday the Volt was safe, but GM may redesign the battery.
In the IIHS side test - the one most similar to NHTSA's "pole test" - the Volt was rammed with a frame designed to mimic an accident with a pickup or SUV. Unlike the NHTSA test, Rader said the impact did not intrude into the battery area.
The group contacted GM following the tests. IIHS crews deactivated the Volt's electrical system, while a team dispatched by GM drained the batteries. GM repurchased two of the cars to be disassembled, IIHS and the automaker said.
In two other cases, IIHS has repeated crash tests for cars and trucks that it judged presented fire risks - the 2000 Isuzu Trooper SUV and 2001 Dodge Grand Caravan minivan.