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You may want to make a battery case ( battery holder ) because you find them too expensive  ( but here are some pretty cheap ones ).  Or even if you are willing to buy them, you may not want to wait for them to arrive.  There have been several projects for building battery cases on instructables, but I think there is room for at least one more.  I also link to what I think are the better instructables so far in a section below.

A flashlight of the old fashion kind is basically a battery case with a switch and an bulb on one end.  This will be my model for my case, a cylinder with the cells stacked one on top of the other.

This is not a new idea, and many people look for a piece of pipe or similar material for the case, just the right size can be hard to find, and the walls are often so thick that the case is bulky.  Here we will make our own tube using the clear plastic from a soda bottle.

A few other elements are required for a complete case:
  • caps for the ends to hold the batteries in.
  • contacts and leads
  • some sort of spring assembly to keep the cells in close  electrical contact

Step 1: Tools and Materials

  • Soda bottle
  • Cells to use in the case
  • Twist ties.
  • Spring plastic foam, or a spring
  • Rubber band
  • Scissors and clear tape
  • Soldering iron.
  • Light weight sheet brass or copper
  • Insulated wire.
  • Things I have forgotten to mention

Step 2: Make the Tube

Harvest the soda bottle for the clear flat plastic you should be able to get a sheet of nice clear plastic; clean and dry as necessary.  You will be rolling the plastic to make a tube, cut it so that the tube will be about ½ longer on each end than your stack of batteries and so it can be rolled into at least 2 turns at the final diameter.
Roll the plastic into a tight roll smaller than the cell you are using.  You should go around two or three times.  If you have trouble after a few attempts then fix a curl in it as follows:  roll the tightest cylinder you can, fasten the cylinder with twist ties, then heat it with hot water ( I used a frying pan on the stove, test with a scrap to make sure it is not too hot ).  After a minute or two put it in cold water to fix the curve in and try again.  Persistence should win out.  When it is in a small tight roll fasten it at both ends, and perhaps in the middle with twist ties.  Now try to fit a cell into the tube.  If the tube is too small ( it should be at this stage ) loosen a tie just a bit and try again.  Repeat this until the cell goes in nicely at both ends.  Fasten the tube in this position with a good amount of  clear tape.  This is basically the technique used in the instructable Chopstick Case  https://www.instructables.com/id/Chopstick-Case-Almost-Free-and-which-perhaps-h/

Step 3: Add Contacts


You need 2 contacts one for the plus and one for the minus end of the battery.  In some cases these are also springs so that they will maintain good contact with with the cells.  Working with spring material can be difficult.  The closest I have found easily available is some spring bronze that was intended as weatherstripping.  If you cannot find that a bit of copper sheet, or even a coil of copper can be formed into a contact.  Perhaps a coin would work for the right coin and cell size.  Solder a wire to it, Place the wire so it will come out the side of the cap, or the middle of it depending on your cap design.  spring bronze is sometimes used in weatherstripping take a look at you local hardware store.  I though about removing the temper from a spring, reshaping it and re tempering it.  Have not tried, seems a bit too complicated, post a comment if you try it.

Step 4: Caps

For the end caps I found some plastic foam that looked pretty much like Styrofoam, but had more bounce, you could squeeze it and it would recover. I cut two plugs each about 1 inch long that would go in the ends of the tube. With an icepick make a hole through each end cap and thread a wire through red at one end and black at the other. Solder this onto a brass contact cut to fit the tube, If you want the brass contact may be doubled over to give it some springiness against the cells, otherwise you are relying more on the foam. Secure the foam in place with an elastic band as show in the photo. In some cases you may find that the foam and contacts alone are enough and you do not need the rubber band ( there are also other solutions than a rubber band, say fish line with a small spring. I melted a grove with my soldering iron https://www.instructables.com/id/Free-Replacement-Tip-for-Soldering-Guns/ to hold the rubber band in place.

For a few 100 dollars more you can get a screw cap: I recently went on an expensive vacation were I got a few bottles of free hand lotion. The cap for this is just a bit bigger than the double A cells I am using. You can epoxy them on the case just as in the Chopstick Case https://www.instructables.com/id/Chopstick-Case-Almost-Free-and-which-perhaps-h/ . This is a more elegant cap if you can find the right source ( try the sample section in a drug store ).

Step 5: Other Ideas

Altoid tins are good for up to 5 AA cells, small tic tac up to 3 AAA cells, and large tic tac up to 3 AA cells.  Again use foam to pad out the extra space.
Remove label from old med bottles, they also work great and a variety of sizes. Doodado

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