The dump truck, at 45 tons, ascends the 13-percent grade and takes on 65 tons of ore. With more than double the weight going back down the hill, the beast's regenerative braking system recaptures more than enough energy to refill the charge the eDumper used going up.
Nice, but it works only in the limited case of dump trucks going down hill when full. In the mines I grew up with, the opposite is true. Those trucks haul their load up out of a pit. An EV or hybrid would still make sense, though, to get the regenerative braking.