Few weeks ago I wanted to take my eScooters LiIon pack and use it for "field charging". The pack says 360Wh - which sounds plenty.
Got me a volt stepdown from its 36v down to 12v (as input to my little ISDT charger): https://www.amazon.de/dp/B07ZV76GGJ?psc=1&ref=ppx_yo2ov_dt_b_product_details
an additional LCD checker to monitor the pack's charge:
https://www.amazon.de/dp/B08L8RDW17?psc=1&ref=ppx_yo2ov_dt_b_product_details
and designed a 3d printed Plate to hold the stepdown and ISDT charger in place

The charger used here is the ISDT 608AC:
https://www.amazon.de/ISDT-Ladeger%C3%A4t-Balance-Entlader-Batterien/dp/B07Z1ZZCLS

One problem in my print: where I wanted to place the Stepdown, I have little "knobs" in place to secure the stepdown. I applied some force to attach them - and with only 20% infill or so - the material below these knobs was too hollow and broke. glued the stepdown in place later...

Creality

Ender-3 S1 Pro

No

0,2

20%