Hi Vinh, I believe the head size dimensions you have listed may be a little off? I’m reading 53mm on other websites for the Nightwatch NI40. I certainly hope it’s 53, as it was a major influencer compared to the Manker U21 for me.
I have the single mode version and I believe it can run until battery is depleted. I just ran it for 23 min and it just got warmish/hot. And that’s tail standing inside ambient temp of 68 degrees. It’s really a nice well made good looking light. I even bought two more for my family members.