Has anyone found any 2x18650 battery waterproof case with DC output? I searched everywhere, the closest ones I have found on Aliexpress are either designed for 4x18650 or 2x26650; the sizes are too big.

I plan to use this battery pack to power a ebike light (Busch + Müller Lumotec IQ Avy E Front Light). I only use my bike for commuting and it is usually a 15-minute ride. I think 5000mhA battery will be good enough to run 15 minutes a day for a week.

I have also considered to design a simple one by myself because I have a 3D printer, but I find it difficult to make a mini waterproof button... I might be able to rip one off from either A and B though. However, before I go down this route, I need to make sure I do not have a better option.