There is a big difference though, Victor.
In a car, the Battery is really only used for the initial startup - once the internal combustion engine is running, it powers the alternator which, in turn, recharges the battery and provides power to the rest of the car (such as headlights, stereo, etc).
If you tried doing such a thing with an Electric car... well, they have actually. It's called Regenerative Braking. The electric engine, when applying the brakes, acts as a generator, using the cars momentum to spin and generate current. This helps to improve the range of the car... but only slightly.
The problem is, an electric generator and an electric engine both suffer from friction and electrical resistance. Thus, even if you had an electric engine that used 25 watts at 1 amp spinning an electric generator that at max could create 30 watts at 1 amp, both feeding from/into a battery, eventually, due to resistance, the battery will deplete, the engine will stop turning, and the generator will stop generating power.