He will only need to worry about additional voltage drop if he needs to extend the cables, not if he is just connecting it to the car battery via croc clips as he said.
IIRC , when I had my Big foot ET jockey wheel motor mover, it must have drawn less than 30 amps, as it had a "Green in-line spade fuse", and had a 3 or 4 meter lead.
My caravan is forward in the drive way, and tucked right up against the fence, so I could not get actually get to the caravan battery box to connect to that, so I used one of those 12 volt Powerpack/starter boxes to run mine. It easily had enough power to run the van backwards and forwards about 15 feet on the drive 3 or 4 times, to manoeuvre it away from the fence, and then drive it out onto the road up a small ramp about 40 feet. I then used to take it off, and put the jockey wheel back on, after reversing the car onto the van, as on my caravan, the jockey wheel is so far forward on the A frame, the handle of the motor mover hit the car before the hitches were aligned.
The only real thing was, it took so long to put it on, and take it off, and then when we had the new impressed concrete drive installed, we ended up selling it, as the slightest bit of damp on the shiny concrete, and it would not grip.