A single car battery lacks the juice to sustain a metal-melting arc between the tip of a welding rod and a piece of steel. (Zombies holding your supply hostage? Welding rods can be made from coat hangers, silica gel, lye, and paper.) So to build my welder, I wired three car batteries in series, then clamped a set of jumper cables between the negative lead of the first battery and a chunk of steel. With another set of cables, I linked the last battery’s positive lead to a welding rod.