Im not saying that an engine can possibly create energy. Energy can only be converted, not created.
What Im saying is that the generator is filled with power, while converting the kinetic energy into electric.
As for resistance of the air or friction....these dont apply in space that may mean that a self chargeable generator could make space travel an everyday experience. In some years though, due to the exorbitant sums required to get a spacecraft in space and the fact that we havent developed that tech enough...+ that oil/petrol companies wouldnt allow self-chargeable engines to be developed. It would be bad for business..