Actually, on lights that use FET drivers, like the BLF A6, it does matter that you use a high-drain cell even if you don’t use the turbo mode.
I did some testing with a light that uses a FET driver (Astrolux S42), using low-drain vs. high-drain cells. I can’t recall my exact results, but it was something like the light was 60% as bright at full turbo, and 70% as bright on all other modes. So, while full-turbo output is harmed the most by using a low-drain cell, all the other modes are harmed as well (unless the light uses a 7135 chip for low modes).
That indicates to me that the low-drain battery is still being stressed. It’s average current drain may be well within its specs, but a FET driver pulses that battery at high current all the time. Output of the light is simply controlled by how long those pulses are.
That said, I still don’t worry about it, and will happily use low-drain cells in my BLF A6’s. Even at full turbo. Yes, it’s hard on the cells, and the light isn’t as bright, but the lower output has a nice side-effect of giving it more run-time. The BLF A6 is a high-drain light, but it’s not super-high like some of the multi-emitter burners.
Anyway, in summary, always get high-drain cells if you can. Or at least fairly-high. The Sanyo NCR18650-GA is a cell where you don’t need to compromise (much) on either drain or capacity.
