This started with joule thief designs I have been working on. It then mutated into this because I work for a battery company, and we are encouraged in experimentation. It uses an over the counter, USB, single cell BMS board for charging and discharging protection, and any color LED you like. I prefer a red LED for middle of the night bathroom runs so it does not wake my wife. I made one for her and she absolutely loves it. My grandson prefers green so that is what he received.

The concepts are basic and if you have any electrical background and soldering skills this is a cake walk to make. I even used salvaged components for everything except for the charger and printed components.