Update: General Motors’ product chief Bob Lutz has a revealed that test fleets for the production Chevrolet Volt would start running as early as next year and that the first customer cars could start rolling of assembly lines earlier than the proposed November 2010 release date. However, Lutz also stressed that GM is not in a race with Toyota to be the first to the market with a mass produced plug-in hybrid vehicle, explaining that the two vehicles will be very different.

The Volt uses an internal combustion engine to solely recharge lithium-ion batteries, which then power an electric motor to spin the wheels. Toyota’s plug-in works in a similar fashion to the current Prius, with both the engine and motor connected to the drivetrain.

Speaking with The Detroit News, Lutz said Toyota's plug-in will have a much shorter electric range than the Volt. However, keeping the technology simple will allow Toyota to launch is vehicle as early as next year, as revealed by the company’s president Katsuaki Watanabe yesterday.

Despite almost admitting defeat in the plug-in race, Lutz reassured reporters that development work for the Volt is fully on track, revealing that a decision has been made on which company would supply the advanced lithium-ion battery technology for the car. GM has been working closely with Continental and LG Chem and will reveal the supplier at the end of the year, likely to coincide with the rumored reveal of the production Volt at this October’s Paris Motor Show.

Original: Earlier this week General Motors released new photographic teasers of its upcoming Volt plug-in hybrid, and now more details of the worst-kept secret in Detroit have emerged from the company itself, detailing the battery pack and describing custom vehicles for specific markets.

The most detailed information yet on the battery pack that will form the electric heart of the Volt reveals that it will be a 16kWh unit, weighing 400lb (181kg) and configured in an elongated T-shape for easier implementation into many different designs, reports Automotive News. And there lies another core aspect of the Volt powertrain's development. GM will be putting the battery pack and its related componentry into a number of "unique vehicles for different markets and tastes," according to Denise Gray, GM's director of hybrid energy storage systems.

By 'different markets', GM almost certainly is eying Europe, and noting its taste for hatchbacks, wagons and other types of cars not favored in the U.S. That means the likelihood for a number of Volt-like vehicles, possibly spanning different body styles and almost certainly spanning several of GM's core brands, will be available shortly after the Volt's release, which is still scheduled to occur in 2010. Exactly what those Volt-like vehicles will be, however, remains one of the few aspects of the program shrouded in mystery.