Long ago I was part of a project that stored vehicle energy in fiberglass rings spinning at insane velocities in a vacuum. The idea was to put the energy not in chemical reactions but into rotational energy. This was coupled out magnetically to the transmission. It worked. Going uphill, it would take energy out; going downhill, it would put braking energy back into the wheel. On flat roads it would provide energy to cruise. A small gas engine supplemented.

My point is some technologies exist but have not been exploited enough.