So where does this energy come from? Seems to materialize out of nothing but gravity effects
The only way to use gravity is to first break free of gravity. That takes lots of energy. Just like when a rocket leaves Earth. It can use the gravity of another planet only because it broke free of ours.
No different than pumping water up a mountain using solar power then use the falling water at night for power.
There is no self-sustaining energy device made by man. Even the sun is slowly burning out.
You are correct about the power the tracking of vehicles gives the government.
It won't be long before they will track your road use by your phone. Even if you're a passenger in a car they will tax you because you are still using the road.