Originally Posted by
x2percentmilk
What you are basically describing is a perpetual motion device. Think about a pendulum, it appears to swing forever, relying on its momentum to move to the top of its arc, and gravity to move back down. What you dont see is small amounts of air resistance and friction at the joint of whatever the string is attached too. This causes the arc to be just ever so slightly less high each swing, less and less until the pendulum stops.
The concept applied here is pretty simple, as you are moving the wheels with the motor you are losing energy into the universe in forms of vibration, sound, and heat (drive train loss, etc). There is no way to regain that energy from the vehicle itself, you need to apply it from the universe (charging station, etc). Its the reason why you see regenerative brakes and not things like alternators charging the battery, the energy required to turn the alternator would even end up with a negative net gain.
Check out the first law of thermodynamics, or conservation of energy for more info.
Also, electric motors and alternators arent very different. If you forcefully turn an electric motor you generate electricity (regenerative braking in hybrids). Taking that and what we have above, ive literally done this in real life.