Like walk said this light is great with the warmer tint options for around campsite use. use the floody extra optic, only costs another 3 or 4 bucks with the purchase and use that. I prefer 2700k to about 3500k temps personally. The e21a I have found is linear driven according to hank’s post here KC1 keychain light is available now . a samsung 35e should be good enough with its extra capacity. just make sure to run the light on low steps in the step mode to maintain running power. If you need duration go with a 21700 light or 26650 one if you can find it.