General Motors is in a dispute with critics regarding its upcoming Chevy Volt, which the automaker touts as an all-electric car but critics call it a plug-in hybrid.

Critics from publications such as Edmunds.com, Popular Mechanics, and Motor Trend magazine contend that the onboard gasoline engine kicks in on the Volt during a hard acceleration, and that makes it a hybrid. GM calls the Volt an "extended range electric vehicle." The Volt features a gasoline engine which acts as a generator for the batteries that power the electric motor. GM adds that it is the electric motor that drives the wheels and not the gasoline engine, which is there to charge the batteries as the car is driving and extend its driving range. But the engine can also drive a secondary generator which provides power directly to the motor.

The Toyota Prius has a similar powertrain setup, and is labelled a hybrid. Its gasoline engine fuels a direct-drive generator that powers the electric motor which drives the wheels. The Detroit automaker had previously gotten in trouble with critics when it rated the Volt's mileage at 230 miles per gallon . The Environment Protection Agency, the arm of the United States federal government which rates vehicle mileage, refused to accept the rating. Mileage figures on electric cars can vary on a wide range as it depends a lot on driving habits. Driven aggressively, the batteries on an electric car can be run down rapidly.

Edmunds.com has been particularly harsh against GM and accused GM of lying. One of its stories has this title: "GM Lied: Chevy Volt is not a true EV."

The Chevrolet Volt goes on sale in the United States next month. A Singapore launch date has not been confirmed yet.