I have a smartphone prototype board right next to me which can be powered entirely from a single (protected!) 18650 cell, and let me tell you that its SoC isn't exactly power efficient. It really seems baffling.
I have a bunch of camp badges there too and while some are really fun boards to play with I wouldn't trade safety for longer battery life with any of them.
Hah I also have a smartphone prototype here powered by a single 18650 and I've already seen one of them turn into a smoke machine because the holder has protruding pins and doesn't fit most protected cells...
Two 18650s also sounds like it would be heavy for a badge
A single (removable) 2000mAh lipo cell, on the low end of capacity for 18650s these days, was a very common power source for smartphones in the 2010s.