You mean, if the starting and ending elevation is the same the hills shouldn't matter? That's not the case. AFAIK, in any vehicle (even in space) the efficien

You mean, if the starting and ending elevation is the same the hills shouldn't matter? That's not the case. AFAIK, in any vehicle (even in space) the efficiency goes down with increased acceleration. Going up a hill is accelerating more (counteracting gravity) and downhill is a negative acceleration, so you end up loosing twice. Ken in a sibling comment claims "50%" which begs the question "compared to what". We'll never be able to reclaim _all_ the energy, but the energy that gets to the wheel is stored back in the battery at 80+% efficiency. Most of the losses are in wind resistance and friction.