Gotta quibble that efficiency claim.

Gensets have pretty poor efficiency. It's not likely to be more efficient than the on-board engine. You get some benefit when scaling up, so one big generator is better than multiple small ones if you have a consistently high demand. That leaves a little room for gains if you'll be constantly recharging multiple trucks. But that will almost certainly be offset by losses in the batteries themselves.

Fossil fuel power plants on the grid just use a much more efficient heat cycle than diesel. It's hands-down better to charge vehicles from the grid or renewable.

edit for the stupid: I am not arguing against battery EVs. I'm just pointing out that charging them with diesel gensets isn't beneficial.