Battery pack casing (Li-Ion 21700)

Custom universal battery casing for a 3S3P pack of 21700 Li-ion batteries, spot-welded together without additional cell holders. All dimensions are shown in the pictures on the right. You will need 6 × M3×4 mm threaded inserts, which need to be heat-set into the housing. There is enough space inside the housing to fit a cheap 20 A or 40 A BMS with a 1.6 mm FR4 insulating plate and some silicone/rubber spacers (in my case, they were 2 mm thick). In my case, this battery was used in a children's ride-on tractor, increasing the capacity from 7–9 Ah to almost 16 Ah, which extended the driving time from hours to days. 😉

⚠️ Safety warning: Li-ion batteries can be dangerous if improperly assembled or used. Always use a suitable BMS and charger, properly insulate the cells and connections, and protect the battery pack from short circuits and mechanical damage. Never use damaged or swollen cells. The enclosure itself is not a substitute for proper electrical and mechanical protection of the battery pack.