I wired up the Adafruit QT Py RP2040 and soldered all the connections. I decided to use the built-in battery compartment. I added a Single Pole Double Throw (SPDT) switch to help extend the battery life. The improved Duo Pop uses on average 30.01 mA. 

I pulled my switch out of an old RC toy car. It is 5.5mm wide which is the exact same size as the space between the battery compartment shell and the outer wall. I used a hobby knife to cut a hole in the bottom of the base and the battery lid for the switch to stick out through. Both the base and battery lid have holes that lined up so I just cut away a little material to join two holes and enlarged as needed.

The improved Duo Pop can also be powered by the USB-C connection on the QT py. I cut a notch out of the lid and a hole in the transparent red collar to have access to it. I made the hole by melting a rough hole using my 3D pen's nozzle and then cutting away extra material as needed using a hobby knife.

I used my hobby knife to scrape off the word "POWER" on the side of the bottom cap and acetone to take off the logo on the lid. WARNING: The acetone will melt the plastic so move quickly.