Just so you know, the “Zener Mod” only limits the input voltage to the mcu. It has no effect on the voltage feed to the led. The purpose was to allow a nominally single cell driver to control 6V worth of led.
They would need to be really tame ones and you would need to use very thin wire too. It can be done, I did it with a DRY driver once. Although the DRY driver had more resistance in it than the BLF drivers do.
The strange thing is the XP-G2 was able to work in such configuration for about a minute before the light started flickering. The XP-G2 didn’t just get killed instantly, so I guess the LED wasn’t actually seeing 8.4V feeding to it?
If you were running a 105C then the 7135s were actually regulating the voltage to the LED, it's just that the amount of heat generated is way too much.
FET Zener mod allows maximum current and voltage to the led. As RMM says, with a Zener modded 7135 driver like the 105C the 7135’s burn off the extra voltage as heat. Likely it was overheated 7135 chips that caused the flickering. With fully charged cells more than 4V is turned into waste heat and they aren’t reliable much over 1V without extraordinary measures that might get you to 2V.
Alright I have a better view of it now, thank you very much to both of you.