Take the 4-D cell battery holder. At the bottom, there will be a wire (or some other connection) bridging the bottom two contacts. You will need to snip this so the batteries are no longer in contact with each other. The positive terminal will stay in place, but the negative spring contact will need to be held in place with a piece of metal and a screw. When batteries are inserted, there should be roughly a 3/8" gap where the spring compresses, just enough room for a short screw. There should be holes in the bottom of the battery holder where the contacts are. Insert a screw through the hole. Hold the spring in place with the metal plate. Fasten the spring in place with the nut on the inside and the screw head on the outside of the holder. Insert a screw through the positive side next to it as well, head on the outside.
(sorry for the blurry pic. Close ups tend to be fuzzy, but you can see the metal plate and the screw inside holding the spring in place.)