The build is indeed a custom one, as it was the case with previous pack. To allow for a smaller ID you place a cell in the middle, then surround it by additional 6 batteries - like in a shape of flower. This way, resulting diameter for 7 batteries will be roughly 3 * diameter of single cell. So in case of 217000's it was smth like 6.5cm; for current build it is even less: approx 6 cm. For that, any tool box with the given specs will fit: 6.5mm ID, approx 22-24cm in length. You have to be mindful though that some of the bottles (like the one I used) have "extenders" -> when these are fitted, they decrease its resulting ID by a bit.
Theoretically, even 20 21700 batteries could have been packed to the Zefal bottle I used (that's Z BOX L, btw), but then there would be too little space for BMS and connectors would be external, which I did not want. If you take a look at my previous build, it had an additional tube attached to it, making the resulting length 27cm - too much actually. And then ofc the weight... given that it mounts to the bottle cage, additional 500 grams play a big role for extreme riding. Hence using lighter and more compact 18650's. Resulting 7A vs 10A does not make that huge of a difference to me, my routes are up to around 40-50km anyway.
Cannot show you the picture of the assembled cells, cause battery is now sealed and opening it might damage the wiring; in that sense, it is not really serviceable.
My idea of using this form factor for the battery was that it should be:
1). Easily transportable (total weight with a nylon pouch and mounting system is 1315g; cables are detachable, so easy to stow away as well)
2). Very quick to mount/dismount (thanks to Fidlock Base + Uni mount that's 1-2 seconds)
Oh, and btw, I considered another mounting option - Ibera cage. It rotates 30 degrees to either left or right and can be adjusted to different diameter of the bottles. However, as it is metallic, using it will scratch the plastic on the Zefal bottle eventually, and mounting is not a quick as with the Fidlock system. For larger frame sizes, probably you could go away with using other, "conventional" cages, but mine is M, and putting the battery there was being a little awkward, not to mention that not a lot of space was left for connectors.
It is a bit on the longer side, but 378WAh, same as TEC.
