Lithium ion battery producer A123 Systems has confirmed it is to bring to market a conversion kit that will turn the Toyota Prius into a hybrid plug-in.

The kit will ship in July through the company's Hymotion subsidiary.

The conversion kit, which has to be fitted by a certified installer, will turn the Prius into a vehicle chargeable in four to five hours via a conventional 120v outlet. It uses a Lithium-Ion battery that supplements the car's existing electric motor, enabling it to run for roughly 40 miles as a pure electric vehicle before it resumes its function as an electric hybrid.

Driving an equipped vehicle 11,440 miles each year – which equates to 20-mile each-way commute five times per week, plus 10 miles at the weekend – would require just nine trips to the gas station, said the company, as opposed to 21 trips for a conventional Prius. The equipped vehicle would also get 105 miles to the gallon compared to the Prius' 47 miles.

A123, which is also being considered by General Motors as a supplier of batteries for its Chevy Volt electric vehicle, will sell the conversion kit for $10,000 in the US.

It is currently working with the California Air Resources Board to establish certification guidelines that would allow it to sell an initial 500 units in California. This would constitute a pilot rollout that would pave the way for a consumer launch, the company said.

A123, which says that its batteries have a life of ten years or more, would not comment on why the warranty on the battery and the conversion kit would only last for three years.