See 18650 & 21700 battery internal resistance cold testing for some results in cold weather for high drain batteries. The Nitecore didn’t did as well as expected on HKJ’s tests, so maybe one of the high drain batteries is better after all, the Molicel P26A and P28A particularly have a –40C min operating temperature, the P26A being easily available. I haven’t seen independent testing of it under low temperature, but if its datasheet is to be trusted it should work well.