Frames for assembling battery packs from 18500/18650 cells

Today I have not just a mini-review, but a micro-review. It’s about some very inexpensive but useful “helpers” for anyone who often builds battery packs using 18500, 18650 and similar cells.

As I said, this review will be microscopic: a little text, ten photos and some conclusions.

I mentioned recently that I sometimes work with 18650 cells, and to make it easier to build packs from them, I bought a rather specialized item: bracket holders. To be honest, I’m not sure that’s the correct name, but that’s what the store listing called them, and I couldn’t think of a better name myself.


The order contained 20 pieces, and the whole lot cost $1.67, so a pair comes to 16.7 cents. You’ll see below why I’m quoting the price per pair.


The pieces are identical, but have a fairly complex shape. Each has an outer and an inner half, and one side has protrusions while the other has cutouts.
In the photo, they’re turned so you can see them from every angle.


Thanks to the cutouts and protrusions, which have a “dovetail” shape, they can be joined in various configurations.
Dovetail joints are more commonly seen in furniture, as well as in firearms and a few less common applications.
The picture shows a corner joint, but there’s nothing to stop you using the same principle for straight joints, too.


As you’ve probably figured out, each pair is designed for three cells. You can use them in 1x3, 2x3, 3x3 or 4x3 configurations, as well as 1x6, 2x6, and so on. Basically, any configuration you like, as long as it’s a multiple of three.


It’s not quite the intended arrangement, but you can also make a 3x4 configuration, with one pack mounted sideways (the one on the right in the photo). This might be useful for particularly “creative” pack layouts—for example, if you need a 5x3 configuration with three more cells connected at the side.


Overall dimensions.
1, 2. Overall length and length excluding the protrusions. When assembled, a protrusion fits into the slot of the next section, so it isn’t included in the calculations.
3, 4. Same as above, but for the width. Photo 4 shows that once a cell is installed, its 18 mm diameter becomes a square with 20.2 mm sides. In other words, add about 2.2 mm per cell to the overall dimensions. The same spacing is maintained between cells in the pack.
5. Width at the narrowest part of the frame. This dimension isn’t particularly important, since it doesn’t affect the overall size of the pack.
6. One side has protrusions that affect the length of the cell pack. The protrusions are about 0.87 mm thick on each side, so the pack will be 1.7 mm longer than the cells themselves.


I’ve listed this dimension separately because there’s a small catch.
The length of the cells doesn’t matter at all, since the halves are independent, but the diameter is critical. I tried several different cells. The branded ones fit without any problems, but the no-name ones were a tight fit. Not terrible, but I did have to push them in with some force. On the one hand, that’s good—they’ll be held more securely. On the other hand, it’s something to keep in mind.


So what’s the point of all this? Sometimes you need to build a pack from several cells. The usual process goes like this:
Take several cells, put them together, weld the tabs, and insulate the assembly with heat-shrink tubing. The downside is that strong vibrations can damage the insulation on the cells, potentially causing a short circuit. The assembly itself is also more “flexible.”

The second option:
Everything I described above, but with X-shaped plastic spacers between the cells. I showed them in my review of the cordless drill battery modification. It’s a pretty good option, but these spacers cost money too, and they don’t protect the ends of the cells.

Using the frames reviewed here makes the assembly neater, stronger and better protected. The cells are also spaced 2 mm apart, making it much harder for them to short against each other.


Here’s a 2x3 pack as an example. These frames are more useful for complex configurations, such as building batteries for electric bikes and the like. That’s also where you get strong vibrations and lots of cells, and heat-shrink tubing alone can no longer hold the whole assembly securely.


As I mentioned above, there are protrusions at the ends. They’re shaped so that the strip used for spot-welding battery packs fits neatly between them. When using batteries with protruding positive terminals, it doesn't work out well, but battery packs are usually built with batteries that have flat positive terminals, and there are no issues here.



That's all. In short, I think this is a very convenient option for anyone assembling battery packs, especially ones with a large number of cells. Simple, inexpensive, convenient—I can recommend it.

As a bonus, I made a short video; perhaps it will make it easier to understand what this is :)