Hi and welcome to BLF, killingtime... aren't we all just?
The only cell (among those I have) the ST50 won't take is the Xtar 2600. Cell length is the issue, as the ST50 rear body tube and tail cap are annodized, so the light is locked out with longer cells by about 1/4 turn. The following protected cells work fine:
Does is have a good throw? I’m looking for a “straight body” 18650 light which throws well. I currently have a Solarforce L2T and the brightness is blinding, but not throwy. On the N-Light homepage they say throw is 200 meters, I don’t know how true is that.