You need to find someone who has both like ToyKeeper or just ask the maker Hank. For the quickest answer, I would ask in a big review thread as I’m sure there are many folks that have both those lights.
From a lot of reading and asking I think more than once, the threads on various runs of D4 may or may not be compatible with the D4v2. It depends on the run. Good luck, though!
Regarding flashlights that can run on different size batteries: I watched a few of reviews on different flashlights, and the same reviewer shows he gets more lumens from a 21700 battery compared to a 26650 from the same torch. How is that so?
First you need a light that is sensitive to the battery power such as one with a FET based driver. Then you pick a strong 21700 battery and a weak 26650 battery and there you go.
Ok, thank you. I thought a 26650 should pull more lumens, and longer run times. I didn’t even think about the mAh aspect. I love this forum, I am learning a lot.
Battery manufacturers can use different chemical mixes to optimize the battery. For instance you can look at the Samsung 30T, 40T and 50E. The 30T has the lowest capacity but the highest amperage and the 50E has the highest capacity but the lowest amperage. Then the 40T is right in the middle.
The 26650 container holds about 50% more volume than the 21700, but they are only made by smaller battery companies and they don’t usually have the best mixes. There is only one 26650 that has 5750mah and the rest are lower.
So each size battery has a range of capacity and amperage. The person who did that test you mentioned probably chose a more powerful 21700 and a less powerful 26650.
Thought I would update this. I ordered the 18350 tube for the d4v2 from mtn hoping the threads would work out, and they did. Fits my d4v1 perfectly, and makes it scary tiny.