If you’d prefer a video example that is more or less what most people on this forum would do for a basic flexible pack, https://www.youtube.com/watch?v=yMLsBxPpj00 is a good example from @ShutterShock.
Edit: I forgot he used precut strips on that, but similar can be done with 30 mm strips cut for each end of each p group.
Got you, now it’s pretty straightforward to me.
Now it’s the time to search for 30 mm nickel…
UPD: okay, that was easier than i thought. Thank you
My suggestion for longevity with actual flexibility: use silicone super flexible wire for the joints and lock the p groups together.
Any flex at the p group level will break your welds or nickel or both. I use tesa tape (the fabric kind not the fuzzy kind) to insulate the cells plus fish paper where appropriate, neutral cure silicone to glue the cells because i think it holds up better than hot glue, and then strapping tape/fiberglass reinforced packaging tape to add more rigidity. Then i like to heat shrink them to seal them up using more silicone to make the group as waterproof as possible and cut out little holes to solder the series connections… then hit the connections with hot glue to seal it back up.
I have used flat braid successfully for the flexible series connections but failures have happened and a few of them have been reported on here. The consensus after the discussion iirc is that the braid just isn’t quite flexible enough and the silicone wire series connections is bomb proof as long as you don’t have anything rubbing… which will kill anything you use to connect. On mobile so no example pics but if you scroll way up there are lots of good examples
Post your progress pics, id love to see your progress. Good luck
Her are some pics i fount that kinda demonstrate what i mean. here i have flexible and non flexible sections on an 18s 8p pack. the non flexible sections are built and the series connections (c in your drawing) are done with flexible braid. its my opinion that the flexible braid can flex to get installed but after that it doesn’t move again. just not flexible enough for how many micro bends and vibrations we run into. ymmv
Then the inflexible sections are connected across the flex point with silicone wire. the lengths here are a bit excessive and shorter lengths would work if the points i was connecting were closer but if you look through a lot of the pics up thread there is usually a significant bend or slack added to the flexible series conductors, it gives the wire more room to move and not translate the vibration to the connection point and also a little length so that if you aren’t quick with your solder and it wicks up the wire you aren’t left with a rigid connection point that will fail.
here is another 18s pack that i made more recently and shows how i seal everything back up with hot glue through the heat shrink and a little better length on the series connections.
Yeah, I definitely will. Already ordered fishpaper/nickel/cells and so on as well as other hardware.
Damn it’s too cool to make your teenhood wishes come true by just snapping your fingers 
And thank you for pictures, i will definitely use them as reference.
Luckily enough, i have spare 10AWG silicone wire pieces from old builds.
And just sharing my thoughts, I am not a native speaker, so I have already forgotten how much language practice esk8 brought to my life in past.
So one of my first boards was a meepo awd with the v3 hubs and first thing i did to it was make a new bigger battery. Was one of the first batteries i made that was half good enough to last but i quickly grew out of it and gave up on hubs being a daily driver in my area.
Bla bla bla was a loaner for a bit but then it’s been sitting half disassembled on a shelf for a couple years now. I check the battery every so often and it just sits at 3.6v a cell happy to retire in place but I’ve gotten bored, so let’s see what i can fuck up.
The battery i made back then was some kinda halfway between a chocolate bar and a flexible flat pack 10s6p and the first p42a battery i made. It was ok but i made it before i found this place and learned so much here that it’s got some flaws.
Also wanted to top box it and see if i can’t get a little life out of that board again and also im bored waiting on the weather to warm up so i can frit my other deck. @glyphiks had some good points about converting a flat pack to a brick so here is the horror show. My use of fish paper rings was spotty when i first made this and im not going to tear off to redo the welds - this is just a junky salvage operation. I did cram some isolation in where i could.
So i found some old photos of when i was making this guy, it was just strapped to the bottom of the board for so long it was no longer a temporary solution. At one point i covered it in diamond plate aluminum, at another i sealed it up in neoprene. Mistakes were made but my heart was in the right place.
So i cut the neoprene off it (not pictured) and here’s what i had, i had painted some liquid electrical tape on the solder joints. 
Also found a lot of dirt had gotten into it from a trip to the desert and generally riding this like I stole it.
Spent a ton of time meticulously cleaning and inspecting everything and it all seemed good so I applied a generous supply of Al tech fold and solder techniques learned from a hobo who lives in a van down by the river and came up with this:
That’ll do pig, that’ll do
Many such cases
What is the type of this black compound u use to fix balance wires?
Nearly. I’m still just a hobo who lives in a tin shed for the time being. If only life were so glamorous to live by a river.
Nice job on the conversion 
That’s hot snot/hot glue/thermal adhesive. Nothing fancy
Speaking of hot glue, is it fine to assemble p groups using it? Was just curious if it is better to use silicone instead.
This is a debate, i fall on the silicone side. Hot glue never holds for long for me unless you put in a bunched of extra effort to clean all the cells which ends up taking as long as using silicone anyway and still has a chance to fail so why the extra steps for an inferior product. If im in a hurry ill use hot glue to hold things in place while the silicone cures and either leave the glue or snap it off really quick.
Hot glue is fine for some, ive just tried a bunch of different ones and they all failed after a while where as i just pulled apart a pack i made years ago and the silicone was still holding up. All the packs i made before when trying hot glue have come apart and long been upgraded to silicone.
This is the best stuff I’ve found so far as hot glue goes and i use it for the wire management or anywhere i may need to remove like on the balance leads as strain relief. Really its the cell wraps from the factory that just won’t stick to hot glue for me - i use it all over other parts of the packs i make that don’t require the extra holding power of the silicone
Silicone i just get some neutral cure of whatever brand is cheapest with a removable nozzle, boss 801 is my current fave as it is a bit lower viscosity and cures softer so it gets into all the cracks and tight places to really stick and seal well
Ymmv
I used to fall into the silicone ideology, but then i tried some Ryobi black hot glue and it changed my thoughts. It’s a fat stick and you need a gun with Hi/low for it to do its job properly. Run it Hi. It sticks really well and stays somewhat flexible, instead of cracking like normal hot glue.
I just like the speed you can go using hot glue
Didn’t stick well enough for me. Once it cooled a little flex on the group would break some of the joints. Probably a skill issue.
It is faster, but I batch them all up and use hot glue to hold them in place until the cure if rushed to get the best of both worlds. If im not in a rush the 6hr skin up time and 24hrs for full strength is fast enough. I dont mind being slow as i have lots of work surfaces and just work on a different bench until they’re ready - a huge luxury not everyone can manage
Just a side note…Any flex causes stress on the spot welds and can fatigue them and even break them over time. Flex should be avoided like the plague, a spot-welded pack must be as stiff as possible unless provisions have been made to allow for the flex and keep it away from the welds.
that’s a really good point, and needs some emphasis. using silicone to glue the p groups shouldn’t be done in a way that allows them to flex. nice large surface areas of contact and tight groupings with consistent spacing along two axis of rotation will keep everything tight tight tight
the ductility of the silicone helps prevent cracking splitting and failure of the cell/adhesive/cell connection as they cycle through temperature changes as well as actually doing its job - sticking them together. i swear i must get the dirtiest cells or something, the only pgroup lasting anylength of time is a little 1s5p i made for a loRa mesh node. and i used cell spacers with it too so maybe a bad example.
I find if the cells are lightly scratched with sand paper it makes a huge difference in mechanical bond strength between cells in parallel packs. I’ve been using urethane or silicone between p-packs.
What cells are they?
Molicel P42A they were stored at around 3.5V
