The Chrysler Group has temporarily pulled the plug on its test fleet of advanced plug-in hybrid-electric vehicles (PHEVs) to fix a battery problem that occurred on a small number of models.

In particular, the Detroit-based carmaker said three of the fleet’s 109 pickups fitted with plug-in hybrid powertrains sustained damage when their prototype 12.9-kWh lithium-ion propulsion batteries overheated, adding that no injuries were reported with all incidents happening when the vehicles were unoccupied.

“This action is being taken to build upon the lessons from the initial deployment and to concentrate resources and technical development on a superior battery,” said Michael Duhaime, global director-electrified powertrain propulsion systems.

Even though no similar issues occurred with the 23 plug-in hybrid minivans deployed as part of a parallel project, just to be on the safe side, the Chrysler Group has also withdrawn these vehicles from service to make changes to their batteries.

“A different battery chemistry will be used in the projects’ next phase, which will focus on grid interaction and improved safety. The complexity of the engineering solution will determine how many vehicles return to service,” said Chrysler in a statement on its website.

The PHEV test fleet program, which is jointly funded by Chrysler Group and the U.S. Department of Energy, kicked off last year and is scheduled to end in 2014.

Chrysler has said that one of the most prominent features of the PHEV program is the ability of some of the fleet’s plug-in pickups to transfer power from their batteries to the grid, which could generate revenue for fleet operators, while the trucks can also link with each other to form independent mini-grids.

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