S2+ lights from Convoy have low voltage protection and fit both protected and unprotected, flat and button top batteries. Just make sure that the max battery discharge rate is higher than what the light pulls on high.
In the S2+ with SST40 and the Convoy 5A driver I use the unprotected flat top Samsung 30Q and unprotected flat top Sony VCT6.The flashlight ships with both springs bypassed for less resistance than just the steel springs.
I mostly use medium setting since it provides the light needed for most of my uses.My light is pre availability of biscotti firmware.
This may be the best factory made S2+
Here in the US genuine 30Q batteries are often on sale in the $3.00 to $4.00 range.
If you have the same version that I do (and I believe you do) then the driver can pull a max of 5 amps. I also have a sst40 equipped Convoy C8+ with the same driver. I use unprotected cells in both because from what I have read these lights have good protection circuits.