This is an easy battery holder I made out of scrap parts. It can hold 1, 2, or 3 AA size batteries and could easily be made bigger to hold more or bigger batteries.
Step 1: Parts Needed
1: Any plastic tube that will fit your batteries snugly inside
2: Plastic bottle cap that is bigger than the end of the tube (any other rigid piece of plastic will do)
3: Small metal spring that is smaller than the tube
4: Aluminum foil
5: 2 electrical wires (stranded is better as it will be more flexible without breaking)
6: 2 clothespins
7: Short piece of thick wire
8: Scrap aluminum (mine is probably between 1/32 and 1/16 of an inch thick)
9: Super Glue
Step 2: Tools Needed
Step 3: Measuring the Tube
Stack your batteries positive to negative in a row (this is how they will be inside the tube). Add the spring to the last negative terminal of the batteries and then add the width of your tube + 1/4 of an inch. This is how long you will cut the tube.
Step 4: Making the Positive Terminal
Next, cut out a circle of plastic from the bottle cap or other piece of plastic so that it fits on one end of the tube as a lid. Then strip 2 or 3 inches of insulation from one end of one of your electrical wires (if using stranded wire, you would want to use solid core wire just for this part and then connect it to the stranded wire with a small 1/8 by 1/2 inch strip of scrap aluminum squashed around the two wires you want to connect; this would be instead of soldering). Bend the stripped end back and forth to form a metal disk that will fit on the plastic lid you just cut. Super glue it in place in the center of the plastic lid and sand the surface to remove any glue that might prevent an electrical contact. This will be the positive terminal. Then cut a small notch in the side of the tube to allow the wire from the metal disk to exit, and super glue the lid in place with the metal disk facing into the tube and the wire exiting from the notch in the tube.
Step 5: Negative Terminal
Now, wrap the end of your spring with aluminum foil so that you get a lump of foil that will fit snugly into the tube but still slide freely. The lump should be approximately as long at the tube is wide. Make sure the spring is centered in the end of the aluminum foil lump. This is part of the negative terminal.
Note: Do NOT use superglue here. You want a good electrical conductivity between the spring and the foil.
Step 6: Finishing the Tube
Now, stack the batteries into the tube with the positive end towards the metal disk and the negative end up towards the opening. Then slide in the negative terminal part you just made and mark where the stack stops. Then drill a hole all the way through the pipe just about an 1/16 to 1/8 of an inch below the mark towards the bottom of the tube (positive terminal). Repeat this procedure for all the different number of batteries you want to be able to use. The hole should allow your piece of wire to pass through.
Note: Drill holes AFTER removing your batteries and negative terminal from the tube.
Step 7: Finishing the Negative Terminal
Take your piece of wire and cut it so that it passes through the holes that you drilled in the tube and protrudes about an inch on one side. Strip 1/4 inch of insulation of the other electrical wire and wrap the stripped part of electrical wire around the end of your wire (the one you just cut) about 1/4 inch away from the end. Cut a 1/2 by 1/8 inch piece of scrap aluminum and wrap it around the electrical wire and wire and squeeze it tight with the pliers. Then bend the 1/4 inch end of wire on top of that and squeeze that together
Step 8: Making the Clips
Now, cut 2 pieces of scrap aluminum (1 for each clothespin) so that they fit on the end of the clothespins and protrude about 1/8 of an inch at the back. Cut this part so that there are 2 tabs at the back end of the small aluminum plates you just made. Then strip the other end of the 2 electrical wires and squash it under one of the tabs on the aluminum plates; then bend the tip of the wire back and squeeze the other tab on top of the whole thing. Now, you should have the other end of the 2 electrical wires attached to 2 aluminum plates. Super glue one plate on each of your clothespins on the inside of the tip. Now you have 2 easy electrical connectors.
Step 9: Finish
This is all you have to do. Slide your batteries positive side first into the tube, stick in the spring, use a stick to compress it, and you should be able to slide in the wire of the negative terminal.