this is a simple holder for size d batteries, I used two to put out 3v, but you can easily stretch or shrink the design as you need it, also you could use the same principle for size c cells. I had a lot of size d cells in the cupboard doing nothing, as they have a much greater capacity than AAA or AA batteries I wanted to use them to power some christmas lights, that way they would last much longer between changes of battery.
Step 1: What You Need
basically its just pipe clips / holders - two u shape screw fix sort (ideally just big enough to go over the batteries and two of the sprung sort, ideally the middle of the clip would be the middle of the of the battery (mine wasn't so I adjusted accordingly, more on that later) .
I just used what I had lying around, if I was shopping you could probably do it all with the sprung sort of clip, which would make it quicker and easier to change the batteries.
Also you'll need some scraps of wood, some wire, some screws. I also used some terminal block connectors and a switch, but your needs will vary.
Tools wise you'll need a soldering iron and a screwdriver
Step 2: The Build
first take your scrap wood, for sizing just lay out your batteries and clips and then trim to size, mine worked out about 9 inches long, and maybe 2.5 wide, it a scrap of pallet wood I think. The sprung clips will form the connections, I found that they were a touch too big so I needed to raise the batteries slightly, I just mounted the batteries on another piece of wood, slightly shorter than the length of two batteries, so that the base of the sprung clip sits under the battery, you can bend the clips to make sure that you get a good connection. Then I just screwed it all in place.
After that I soldered a wire to either end (on the sprung clip connector). I kind of wish I'd drilled a hole in the clip to mount the wire,as it would have made a better join. I could have held the wires in place with the same screw that held the sprung clip / connector, but I went down the soldering route.
Essentially that's it, I put a switch and terminal block connectors in as well, which I held in place with hot glue.
Step 3: What I Use It For
I had a load of these LED light strings that run on 2 AA (or maybe AAA, I can't remember), I took carefully took one apart, I got rid of the switch but kept the resistor on the negative side. I normally find that the cable is slightly shorter than I need so I got out the soldering iron again and extended the length with some doorbell cable. I can now screw the newly extended string into the terminal block and I have a working string of lights.
Not that impressive so far, but at least I can use up some of the D cells that are knocking about in the cupboard.
However, it gets better
I took apart another couple of string lights, as before I kept the resistors in place and used some more doorbell cable to extend the length.
Now I can run these in parallel, all the negatives get screwed in together, as do all the positives.
So instead of using 6 AA batteries (which I don't have), I can now use 2 D batteries (which I do have).
I haven't tried running more than 3 sets of lights like this, I'm not sure how many it could take, I assume that it would depend on how much current each string draws, however the 3 sets I have seem every bit as bright as the did when powered individually, I'd imagine it could take a few more strings but 3 is all I need.
Step 4: Update
I now have four strings of light running from this set up and all still nice and bright so that's two D cells doings the work of 8 AAs, result!!