I’ve built a new gadget to store electrical energy in lithium batteries for an outdoor application. It’s very simple, and it all fits in a weather tight enclosure. Here are the circuit drawing and a photo.
As you can see the output is 5.1VDC, just right for a webcam or other SoC board gadget.
Of course once a build starts there is always a problem. The 18650 batteries I chose are flat tops. The battery holders have riveted connectors that were not contacting the positive terminal of the batteries. I added a small nut and bolt through the center hole of each positive terminal, with the screw head facing the battery.
By wiring pairs of batteries in series we get about 7.4V, 4 pairs of batteries in parallel increases storage capacity, and the buck converter provides regulated 5.1VDC output. The charge controller used is designed to charge 7.4V batteries up to about 8.4V.