[mulletbum]

The same way every other battery replaceable product controls for it, they write it on the housing.

[aetherspawn]

The polarity of the 18650 cells themselves is not that obvious either. Each manufacturer marks their cells differently or not at all. Many cells are flat on both sides and do not have a "nipple" indicating the positive side.

The fuse solution mentioned here by the manufacturer sounds like a good solution.

[vallettea]

yes but there is a fuse per cell so even updisde down there is no fire hasard: https://docs.gouach.com/eco-designed-batteries/additional-be...