Anyway... they do perform as advertised -- when benchmarking, it gives > 1 hour on 420lm. Not bad. it also has low light modes, like 65lm and 3lm. Using the low-power modes will make battery last significantly longer, right?
Well, not at all. I use it for horseback riding, which means in weather around 0 celsius (freezing). The lamp will behave quite nicely if I switch it on and let it on. It will start in 750lm mode, heat itself, and continue in 420lm, warm, for cca hour. But if I try to extend battery life (or try to be nice to my surroundings) by keeping light down, the temperature will go down, and when I then attempt to use high mode, it will fall to 3lm mode, or even fail completely. Usually it is possible to restart it in 3lm mode after few minutes wait. Ouch. (Switching to 750lm mode is too easy; that usually kills the light when cold. Selecting 420/200/100lm is not possible without going through 750lm mode; that does not help, either).
I have had light failing within 10 minutes -- go low for 10 minutes in cold weather, then switch 750lm mode, then battery trips.
Would some kind of isolation for the light help? Would the results be significantly different with better battery? Is NiMH better than LiIon for this? Is someone doing more realistic benchmarks that cycle maximum mode, but let the light cool down between tests?