This is a remix of the 18650 battery holder for the (tr)uSDX. It allows for a 3S BMS off Amazon (~$2). This allows for safe cut off when low voltage is hit, and also for safe charging and balancing off a ~12v power supply. I tried to allow enough space for the balance wires needed from each cell and the BMS fits nicely in the cutout with shrink wrap.
The BMS needed is listed here:
https://www.amazon.com/dp/B07DYS6RJJ?ref=ppx_yo2ov_dt_b_product_details&th=1
The battery holder is the one listed for the official model. You have to be very careful inserting it as the wire that runs underneath drags and can tear. Also I have found no safe way to solder the balance wires as the heat instantly melts the cheap plastic holder. I had started working on a complete 3D printed case that doesn't use the holder. If there is any interest I may still.
https://www.amazon.com/dp/B092TG8Y2X?ref=ppx_yo2ov_dt_b_product_details&th=1
The author remixed this model.