This battery thing makes no sense for a pinball. They are testing a "black box" in a car with the proper power source - a 12V DC battery. If you want to see if a coil is pulling in for a pinball, you could mimic this by simply hooking jumper wires from your transformer to your coil. You would probably only have to hook the hot line up, as you are probably safe in assuming your ground line (yes, I know, return line) is intact.