I had this nice Craftsman® cordless drill for years. It was a gift from one of my brothers and it served me well for a long time. After repeated use and abuse, the battery stopped holding a charge. I decided not to buy a new battery and convert the drill to be powered using a plug meant for a cigarette lighter socket. I was inspired by Bikeframe's instructable Run a Drill of a Car Battery.
Step 1: Removing the battery cells
Carefully I pried the positive terminal off the top of the cell. I soldered a wire to it and put it back on the plastic part that held both terminals. To replace the cell that originally held both terminals, I cut a piece of plastic conduit. I cut the plastic conduit with a hacksaw and smoothed the ends with sanding paper. I also drilled a hole to pull the red wire from inside the plastic conduit. Using crimping connectors, I connected the plug wires to the red and preexisting black wire of the battery. I also tied a ty-wrap around the cable and tightened it to make sure that nobody would pull the wires from inside the battery by accident.