It will definately work as long as there is no significant loading put on the machine i.e. as long as the wheels are off the floor then they will power the traction motor(s) without problem.

In this instance though the intial diagnostics can simply be done with the key on and line contactor in, without a real need to load up the machine.

Take some power pallet trucks these days and you'll find that they get there 24 volt power from two 12V gel type batteries the same as those you could fit to a car.