A portable, battery-powered sprayer for dispensing two liquid products at the same time includes first and second nozzles which receive first and second liquids and first and second air supplies. In an example, the holder includes a bolt assembly having a first end to attach to a vehicle and a second end to quick release a support plate for holding the vehicle license plate. A current flowing through the current return path is sensed to execute feedback control to the output of the high-tension power supply. The load is then removed from the transfer unit outside the mine so that it may be advanced back into the mine to retrieve another load.