Hi everybody,
As I am currently building a 2nd battery for one of my eFoils, I thought I might share my way of designing and building such a battery pack. Hoping this may help some of the beginners to get into that (sometimes a bit frightening) topic.
First part:
Feel free to share your thoughts and what you would do differently 
Excellent video ! thanks for sharing. I realize that I assembled my Li-Ion cell nickel strip first in parallel then in series like you mention. Do you really think I need to remove restart from zero my pack ? I use nickel 0.2 10mm on 21700 (40T3) on 12S8P.
Don’t worry too much about that, keep it in mind for the next pack 
thanks @ludwig_bre I will share my assembly in few days when finalized. Thanks again for your great video.
Good watch. Trying to digest as much as I can before building a battery.
So if I build a 12s battery and just want a single pair of cables and not split it into 2 6s packs what are recommended chargers? Just any of the million 50.4v Chinese chargers? What amperage should I look for? I will run a bms for charging, just not discharging.
A built in bms or a >=12S Charger, like ISDTx16 (not cheap).
So use a 50.4v charger with a BMS?
These questions will be answered in the 2nd video 
But already as a teaser:
Option 1: Build charger yourself from PC/Server PSU and a Step-Up regulator (my way)
Option 2: Buy cheap chinese charger
For both 1 and 2 you need a BMS or at least a balancer, either external or internal.
Option 3: Buy a 12S Balance Charger
Guys, sorry for the comment that is just partly related to the topic.
Ludwig, thank you for the video. You seems really experienced in this field. So maybe you know how could I restart the BMS or current settings and memory of the Lift Efoil battery?
Or I need to build mine from scratch and it would be easier? 
Sorry, no experience with Lift
There was a topic here about that though, maybe there you find some information:
Thank you @ludwig_bre, this was super helpful, finally I understand more lol… looking forward to Part 2!! Could you please share the STLs for the 3d printed holders if you can? thanks again!
Part 2:
Feel free to share your thoughts and what you would do differently
Sorry for the inconsistent use of “battery” and “cell”. Actually cell is the individual 18650 cell, battery would be a assembly of multiple cells.
3D Files of the holder I used:
https://lbre.de/hp/fs/20S7P.rar
Thank you @ludwig_bre for the video and the STL files. Your instructional videos are awesome!!
Excellent video, thank you
An excellent complement to your video is this 15 page detailed battery building guide 'Vincent's build - #60 by Vincentbraillard written by @Vincentbraillard
that is:
Hello,
Thank you @ludwig_bre, great tutorial !
I am planning to build my 14S10P battery pack from 21700 cells.
Maybe you have made battery pack from 21700 cells with W pattern? 
It would be great if someone can share 3D file of holder, trying to draw frame for 3D printer with Fusion360 but it not easy program as paint…
Hey,
No, I have not done one yet for 21700 cells.
If you dont want to model a holder from scratch, check this SCAD-based parametric holder.
Basically just input the measurements into code, click “update preview” and then export as STL.
I recommend to set “slot_height” to 0.
Make sure to print a small size/fit check first to ensure tolerances match
Also make sure to read the console output, for non-symmetrical packs it will tell you to also export a mirrored version for the other side of the pack
I used the ones from the link below, they are good quality and work well.
10Piece 10S2P 20X 21700 Battery Holder Bracket 21700 Spacer Assemble for 36V 48V Electric Bike or Escooter Batteries Use
https://a.aliexpress.com/_EjISESX
Matching 0.2mm nickel strips for this pattern are hard to source and expensive at the moment.
Thank you for quick answers
Somehow managed to draw my pack holder from scratch using @ludwig_bre tips:
