A shrink wrapped battery pack. By Lee Davison.

I have more than a handfull of D cell NiCd battery packs that were rescued from emergency lights that were being replaced. They were tested and four of the three cell packs found to be still good. The thin wire tails were removed and thicker wire used to make these four packs into a twelve cell pack.

This loose pack of groups of cells needed some way of being held firmly together. Insulting tape is not really man enough for the job and the big reel of duct tape seems to have mysteriously disappeared yet again, so I was looking around for something to put them in.

While searching for inspiration for non-tape a solution, or the absent roll of duct tape should I chance upon it now I wasn't really looking for it anymore, I happened upon a recently emptied two litre drink bottle. It looked about the right size to hold a few D cell packs.

The bottle was marked as close to the curved ends as possible and the ends removed. The inside of the bottle was then washed to remove any remaining drink residue and dried.

Comparing the bottle to the pack it became clear that three D cells in a row were just too wide to fit across the bottle but three cells staggered by half a cell was quite a good fit.

To make all four packs fit one of the end packs was broken and reconnected in a V shape to sit at the end of the other three packs. The four packs were then slid inside the body of the drink bottle.

Soft drink bottles are made from polyethylene terephthalate and have the handy property that they shrink when heated. Now that the cells were inside the body of the bottle it was just a case of heating it up to make it shrink round the cells and hold them together.

To do this a 1600W hot air paint stripper set on low was used. First the ends were heated a little to make them turn inwards, then the top and bottom faces were heated. After this the sides were heated before returning to heat the ends to enclose the pack.

The polyethylene terephthalate shrank with quite some force as well as some creaking noises as it pulled the cells together. Unfortunately I didn't quite keep all the cells as close as I would have liked and the V shaped end pack pulled away a little from the other three packs. Not to worry though, if it becomes a problem this cover can fairly easily be cut off and the process can be repeated using another bottle.

Using PET bottles like this makes a quick and durable cover for batteries and it holds them more securely than just tape or ties would. Different sized bottles should work just as well with different numbers of different sized cells. If there is room it should be possible to include some insulating plate with the cells that can be used for mounting the enclosed pack.

Last page update: 1st July, 2011.

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