I wonder how the UI works? From the illustration it looks like you have to click through all the modes before the light turns off. I hope this is not the case.
what would be a good choice of 18350 cell for this, xtar 18350 850mah unprotected, BASEN 18350 800mAh 12A. Trustfire TF 18350 Li-Ion 1200mAh Button Top 3.7v Unprotected, EFEST 18350 Batteries 3.7V Li-ion 800mAh IMR, my guess unprotected would be best.
Note they are somewhat ‘old’ - four/five years. There has not been much evolution in the 18350 format but more recent cells may have a bit more capacity (those test at 700 mAh). Make sure you buy new ones because LiIon cells do age even without use - or so is my understanding.
with the 18650 tube on the S41S my button top Samsung 30Q’s are a press fit and even stripped a bit of the shrink-wrap off of one.
worked OK just too wide for the extension tube. Same with protected 18650’s
they work fine in the S41 extended tube