Comment by Animats

That's interesting. It demonstrates that regenerative braking really works. The energy you expend going uphill, you mostly get back going downhill. The energy you expend speeding up, you mostly get back slowing down. His tests were a round trip, so start and end altitude are the same. And he kept a fixed speed on a freeway, so there wasn't much acceleration energy expenditure or energy loss into friction brakes. You don't get drag or rolling resistance back, so that apparently dominates. Those don't vary too much with load.

Nice result.