The first fully electric mining dump truck in New Zealand is now up and running at Blackhead Quarries Logan Point Quarry in Dunedin. This site extracts and crushes rock near the summit and carts down to stock piles closer to the road. The cart is 1.7km with a vertical drop of 150m for around a 9% average slope.
Running uphill empty the truck uses 5% of the battery capacity.
In early trials the battery regeneration achieved running downhill with a 30 tonne load, is closer to 6% of battery capacity.
Not quite perpetual motion but a great result so far.
On flatter carts and other duties around the quarry the regeneration is less. Overall the truck will still need charging.

The truck running uphill empty using 210kW, at a speed of 20km/h

The truck descending loaded regenerating 176kW, at a speed of 12km/h