This may be old news to many of you but a friend of mine recently gave me a bunch of old laptops to recycle and I (VERY CAREFULLY) dissected the batteries and they were just chock full of 18650s, most of them with 2000+ mAh. If you want a source of a bunch of them for basically zero cost, could be worth a look, especially if you have a laptop that is broken for some reason that isn’t related to the battery.
I followed this video
I also bought one of these thingies:
And with that I took the best of the salvaged 18650s, stuck them in my uConsole, and then I keep the extras charged and available as backups in the powerbank. The trick is finding a way to store 20+ 18650s without them accidentally shorting out by touching each other the wrong way.