Chrysler Group said it had temporarily sidelined 109 trucks and 23 minivans in plug-in hybrid test fleets due to overheating batteries in some of the pickup trucks.

The automaker, which on Monday opened a new 33,000 sq ft office in downtown Detroit, told Reuters three Ram 1500 pickup trucks in a fleet of 109 equipped with plug-in hybrid powertrains sustained damage when their prototype lithium-ion batteries overheated. There were no fires or injuries and the incidents occurred when the trucks were unoccupied.

Chrysler spokesman Eric Mayne told the news agency it was not known how long the test vehicles - out with 16 municipalities and utility companies in 20 states - would be sidelined but the duration of the truck and minivan projects were not being extended beyond 2014 as planned because of the suspension.

The pickup truck testing began in the third quarter of 2011 and the minivan testing began in April.

Reuters noted the tests were being funded jointly by the US Department of Energy and Chrysler. The automaker's share of the funding is US$65.2m and the DOE's is $58m. The pickup truck project is expected to cost $97.4m and the minivan portion, using Chrysler Town & Country minivans, will cost about $25.8m.

The batteries for the project were supplied by Electrovaya, based in Mississauga, Ontario, near Toronto.

While the trucks and minivans are sidelined, Chrysler engineers will work to develop a "superior battery," Michael Duhaime, Chrysler's global director of electrified powertrain propulsion systems, said.

In the next phase of the programme, a different battery chemistry will be used, Mayne said, adding that "this is normal product development."

The fleet of trucks and minivans have accumulated 1.3m miles, Chrysler said.

Setting these tests apart is that some of the pickup trucks are being tested for their ability to create "reverse power flow" from the batteries in the vehicles to the electrical power grid, Mayne told Reuters.

Also, a long-term goal is that eventually vehicle batteries can help power a variety of electrical needs in homes and businesses, particularly during peak demand on the power grid, when costs are highest.

Chrysler said the pickup trucks with the capability of transferring power to the grid from the batteries are the first factory built vehicles to feature this technology.