>>2769711I have a couple of those generic ones you posted floating around. They run off 3x AAA but mine came with a sleeve for each to run 18650s in them if you want. Buy a clearance power tool battery and get a handful of LG or Samsung cells for cheap.
Also a few years back I got some $5 little lipstick sized power banks from Walmart that were a single 20650 cell inside and those cells fit perfect.