Chevolet Volt and EV-1 battery packs side by side.

A 16-kilowatt battery pack for the Chevrolet Volt (right) is displayed next to the original EV-1 16-kilowatt battery pack at the GM Battery Lab in Warren, Mich.

John F. Martin/General Motors

The E-Flex Battery

The E-Flex battery is a 400-pound (181 kilograms) advanced lithium-ion battery that generates up to 16 kilowatt-hours of electricity.

The advancements in battery technology that have made these kinds of devices possible in recent years explain why a car on the E-Flex platform can do what it does. The EV-1, for example, used a lead-acid battery pack that had the same power output as an E-Flex-powered vehicle, but weighed about 2,200 pounds (998 kilograms) more.

The E-Flex battery is also flat, unlike the cylindrical lithium-ion batteries used by most cars of its type. Flat cells take up less space than cylindrical cells, so that more energy can be stored in the car's battery pack. These cells are also easier to cool and condition, since fluid can flow easily across a flat surface.

Unlike conventional batteries that are simply placed into a car's engine bay, the E-Flex battery is so large that's it actually built into the car itself. The T-shaped battery runs through the center of the vehicle between the front and rear wheels, with the top of the "T" under the rear passenger seat. This keeps the battery safe in the event of an accident.

Still, the platform's uniqueness creates challenges that GM must face.

"The heart and soul of [the E-Flex platform] is the battery, with a vehicle on top," said Tony Posawatz, the vehicle line director for the Chevrolet Volt. Engineers know how to design and build vehicles, he said. "But fitting the battery pack, heating and cooling, the types of materials used … that's all not known."

Unlike hydrogen fuel cells, the technology is one we won't have to wait for. "The infrastructure is already in place for electric vehicles," Posawatz said. "Electricity costs one or two cents a mile, versus 10 cents a mile for gas right now."