Re: Li-ion in winter
I think I'll put my 18650 lights away soon and switch to my lights that run on Lithium primaries.
Depends how you carry and use them, of course, but I think most users really shouldn't put them away. If the weather's cold enough to be a real problem, you probably have on a coat long enough to cover any lights on your belt, and anything in pants pockets or inside coat pockets should definitely be fine. Maybe if you carry them in an outside pocket of a coat...
But I used Li-ion-powered flashlights routinely last winter, including one carried in an outside pocket, with occasional subzero weather, and experienced no trouble -- maybe usable capacity and/or current did drop some, but nothing I could even notice. Never messed with -20F, though, and that may be a whole different ball game.
But remember, if your light can cool off while it's in your hand being used, that just means you need to go to high mode! (If you're already in high mode, you need an SST-90 light, and/or to move away from Alaska, Canada, or Siberia.)