Case is printed from 3 parts, they each have a seal in between and way, way too many little m2 hex screws and nylocks keeping it together. The connectors are 1.3€/pcs from AliExpress and (supposedly) waterproof as well.
I used the LG M29 18650 cell, chosen because it was available, had good enough specs and cheap. about 2€ in a group buy from Nkon. They slot nicely in the case, which holds them snugly so no worries about them shifting or rubbing things.
For welding the nickel strips to the cells I used the classic “big battery & big solenoid & arduino” method, worked great.
Wiring the whole thing to the BMS was a bit tedious but worth it, end result is a nice module that has a charging port and a power port.
Going by the ratings of the cells should do 18A continuous and 30A peak. BMS is limited to 30A continuous so it’s good there. I wanted to stresstest the battery since, again, I want to live, but didn’t have any good testing load. The solution was plugging it into my DIY e-scooter, setting VESC battery current to the testing value, and riding around with the throttle pegged and adjusting speed with disk brakes. Those got a bit hot:
Worked great, battery dealt with continuous 30A current for ~5m, limiting factor was the cells getting hot. The onewheel won’t have such loads anyway, so great!