Ryzbor, if you mean to use some ∅22mm Convoy SST-40 linear driver (12 groups or 4 modes) in a Manta Ray C8.2, could work. The drivers may need some modification to work properly with 2S cells, but if they're built with the same parts as other recent Convoy drivers they'll likely straight work fine. Check the Convoy XHP35 Driver Analysis / Testing / Schematic thread, onboard linear regulator investigation here.
The increased voltage drop in the MOSFETs could cause trouble, improve driver cooling as much as possible.
In my experience, though, you can place your multimeter's probes over the resistor pins, and blow some air with your mouth while looking at the multimeter's screen. Even if subtle, that will reduce the resistance 1 - 2% and will give you confirmation that you are peeking at the right thing.
BTW, if someone wants a bit of flashlight sexyness and toughness at the same time, you can get that C8.2 in red
I guess the tube for the 2nd battery is not availble, though. https://www.aliexpress.com/item/32953188982.html
About robust hosts, as a fan of AA lights: Convoy T2, Jaxman E3, Sofirn SF10 (Alonefire X360).
