The above picture is of my electric generator. On the left is a motor and on the right is a generator, when powered is applied the motor turns the generator, the generator will put power back into the battery. I tested the output of the generator and it puts out about 1.2 volts. when I ran it for 5 minutes it lost no voltage and after a break, I ran it again for about 10 seconds and it gained 0.2 volts.
The next day I ran it for 10 minutes it lost 0.75 volts. However I think that this is because of the size of the magnetic field. The bigger the magnetic field the more power it will put out.
In conclusion this would work in theory, as long as you have an efficient motor and a sufficient magnetic field.
