Miloslouis, you don't need to, and for safety reasons should no try and read voltages while the truck is in motion [other than lift or tilt], also you will not get as accurate a reading, and hydraulics's stalled to deadhead puts more load on the battery than will any sort of driving. I would not want to be responsible for some newbie driving over a pedestrian, because they were watching the voltmeter instead of where they were going.