FWIW… I have the T4-7C 1000mA version of the Convoy S6 (FastTech sku 1319303). I also have those exact same protected Pansonic 3100 mAh 18650 cells. The batteries just barely fit, and I would even go so far as to say that for all practical purposes, they do not fit. It’s an issue of girth. When I first got this flashlight, I was able to shimmy one of these Panasonic protected cells in. The next time I went to swap batteries, I tore the plastic coating on the battery. That made me think that it’s too tight of a fit to regularly use these batteries in this body. (Now I have some heat shrink tube and unprotected cells on order.)
Furthermore, I also have a bunch of the Sanyo protected 2800 mAh cells (FastTech sku 1143804). These are definitely too fat for the S6; they won’t fit under any circumstances.
Having said that, I really do like this light. I deliberately bought the lowest-power version for my wife and I to use in the middle of the night when taking care of our newborn. (This was my solution to this question.) Pointed up at the ceiling, on low mode, it makes enough light to change diapers and prepare bottles, but not so bright that our night vision is ruined.
I also have a Convoy S3. I like the knurling on the S6 better, but I like that the S3 can use protected cells. Another minor quip with the S6 is the smaller button size versus the S3. Now I also have an S2 on order. 