If you had 4 on your car you would need 4 battery packs and you would never capture enough energy from braking without plugging the vehicle into a wall.

This Electrocharger seems to be capturing energy and is using it to help accelerate the car. Otherwise the energy from braking is just lost as heat and cannot be reused. From the diagram on their site, when braking, the Electrocharger is acting as a generator and storing the energy during braking when you let off the gas.

It's kinda like using a spring...for you mechanically minded people...hint hint.... during braking you are compressing the spring and then when it's time to accelerate you release the spring and use the force as the spring is uncompressing as you accelerate the vehicle.

However, it appears this is done electrically in the case of the Electrocharger.
I am not selling their product...this jsut makes sense folks!