I have used a variant of this camp lantern for about 12 years now.
It has high function, is utterly dependable, easy to use, and goes for about a week the way I use it, on a set of 4 AA batteries. What it lacks is rechargeability, and use of lithiums. I’ve not tried sinking it in a pan of water. Notwithstanding, I would buy a BLF version just cuz, though being metal (?), it would probably weigh twice as much.
Also thinking plastic should be considered due weight considerations, and also cost. Assuming reasonable durability, but the lighter it is the less force acting on it to cause damage.
Agreed with you on the 21700 size. No need for the extra diameter or weight in this case.
Maybe I should make a left turn and throw something together to test some concepts, and enter it in the Old-lumens hand made light contest at the same time.
Stability when standing the lantern on the end is important. However, I don’t believe that is alone is a good enough reason to choose a 26650 cell over a 21700. Correct me if I am wrong but it seems to me that 21700 size cells offer greater capacities than any 26650 cells.
Maybe it is more important to use a 21700 cell for greater capacities and then just make the standing end of the lantern enlarged?
I agree on that the 21700 is a better (more modern cell size with 5000mAh capacity) choice, and the plan to have the LT1M with a magnetic base, will be easy to have a flat base stand that sticks to it included. (already working on it.
With 21700 we could achieve bit narrower profile. The final shape is very important at least for me, I would greatly like something similar to the recent Nitecore Campbank lantern, which is more or less flat and can be easily worn even in pocket.