My current means of powering things is USB rechargable batteries. I have a about five of them that range between small 3000-5000mah ones to a big 20000mah interstate battery jump starter pack. Is there a device that lets me add all their power together into a centeral power source so I don’t have to keep swapping them out?
Sure, but you probably shouldn’t build a DIY battery pack out of salvaged 18650s of varying brands, capacities, and conditions unless you really know what you’re doing because that’s dangerous if you get it wrong.