A report from the Boulder, Colo., firm that built the Prius prototype said the blaze was instead caused by loose electrical connections that set fire to the vehicle's upholstery, and not by the sophisticated lithium ion batteries it carried, The Los Angeles Times reported Saturday.

The news came as a relief to electric car supporters because lithium battery technology has been under a cloud in recent years due of fires such batteries have caused in some laptop computers.

The modified Prius was one of 10 owned by a South Carolina electric cooperative and was built by Hybrids Plus of Boulder, the newspaper said. The company took a standard Prius and made it into an all-electric version, which isn't expected from Toyota until 2010.

The chief executive of Hybrids Plus said the fire was caused by "an assembly problem."

"I was worried that this would turn into a major incident, but actually most people seem to understand that this was an incident that didn't involve the batteries," Felix Kramer of CalCars.org, a California advocacy group, told the Times.