I use AW IMR 16340s in my S10 (non-L2 version). They work fine.
I have:
- 2 pcs. Sibeile 600 mAh "Li-Mn" cells (which behave like, and are probably just falsely labeled, unprotected Li-Co cells)
- an AW IMR 16340 cell (550 mAh)
- some unknown brand LiFePO4 cell (yellow/blue full color label, not plain shrinkwrap)
all of them unprotected cells, and all of those work fine in my S10-L2. IMR and LiFePO
4 do make a difference in the highest mode. If you're not using that much, go for the highest (real!) capacity ones. Protected or unprotected isn't much of an issue in this light, as dimming of the higher mode(s) is a good way to indicate battery status.
Battery length is the thing to worry about, some of the longer (protected) 16340's may not fit. Width-wise no issues, but sadly 18350's don't fit.