To CSpence up above:
Thing about the TOOLvn--it's a wonderful light and a great WOW light. But the 10440 battery holds *very* little capacity. You are not going to be able to use it on anything like high for very long.
Part of the problem here is that Li-Ion makers lie about their capacities. I mean, I hate to put it so bluntly, but that's basically it.
So the top end for a quality 16340 IMR is going to be around 550mah, maybe 600mah, not the 700 that some print on their labels.
And the capacity of a 10440? No way is it 400mah. I will be amazed to see that any of them have more than 200mah, 250mah tops.
So you should figure that the 16340 format has about 3 times the capacity of the 10440 format.
Run times will be very short for the TOOL. A great back-up light, a great show-off light, but not the one to get you home.