It’s true that the truck’s batteries never have to be recharged. But the truck is still “consuming” energy, specifically the gravitational potential energy of the ore.
So the laws of physics still hold. There is no free lunch here. It’s a great way to power the truck, nevertheless.
From the article:
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.
Also the energy to fill the truck will be greater than any recharge you can get coasting down hill.
The system only works when the machine has a hill to go up and down. How efficient is the machine on a flat surface all day long, where it can’t use gravity to charge a battery?
I’ve yet to see a story on an electric vehicle where there isn’t some significant omission about something, in order to make the product the next greatest invention.