I believe my jump stater unit is a made by goodall, will do both 12 and 24 volt, engine driven, pretty simple concept and really handy to have on the service truck. The issue with using small batteries to crank anything 24 volt just enough to get them started is frying the starter solenoid and then having to take the starter off and get fixed or replaced completely, low voltage kills more 24 volt starters than anything and as of yet in this thread I've never seen that mentioned so I though I would.
As for frying electrical components via jump starting with excess voltage, things must have been hooked up wrong, a lot alternators when charging correctly for 24 volts will put out up 28-29 volts on the machine itself, especially if the batteries are very low or nearly dead. I'm not sure even computerized machines know if the alternator within the machine itself is charging the batteries or if your using a jump starter unit or even a welder to do the jumping with as long as you hook things up correctly. Done it thousands of times with many computerized machines and never yet taken a computer out or fried anything. But I have destroyed many starters over the years with low voltage and trying to crank it and get a machine going, maybe not on the spot, but over time trying to crank it when it barely rolls over..................will eventually get the starter. So after many thousands spent on starters related to low voltage, I did invest in a used jump starter unit, I think it paid for itself the first month from saved downtime alone.
We have also swapped batteries on most machines, to top thread semi batteries, that way, no matter where we are at, or what machine we have, we can if need be, switch batteries out on a dead machine with even those off the service truck or spares we keep on the service truck, then figure out which battery is bad, [usually a dead cell in one battery] and charge the other good battery and put it back in the machine along with a new good battery or a new battery, whichever we have on hand in the field. This whole concept of every machine having their own specific battery size and dimension and needing that specific battery was enough to put me over the edge with so much wasted time.