I have a Convoy S11 I got from Lifetime17 which takes 2 x 26350 cells and they hold up longer than 16340 or 18350 as does the nice copper heat sink Rich puts in the S11 and the S11 is a very nice quality housing.
Used in flashlights and other devices. Model: 26350. Capacity: 2000mAh. Usage of this battery is at your own risk! · DO NOT short circuit intentionally or unintentionally. · DO NOT solder onto battery, spot weld only.
If you want a more compact host ask Lifetime17 for a S2+ and you can use 2 x 18350 rather than 2 x 16340 cells.