For initial testing, I've been using an unlabeled battery from an conference badge I had lying around. It just happened to have the 2 pin JST PH 2mm female connector. I checked the polarity and voltage. Voltage was correct, but black was positive and red was negative. So I traced the wire to the battery protection circuit and it had the correct plus and minus symbols to back my findings. I charged it up and plugged it in... then it powered right up. Ran my test code without issue. I was a bit surprised, not sure why I was expecting something to fail.

Since I don't want to rely on that old battery, I started to search for one online. I wanted something that would last a few hours, I decided to look for a 1500 mah, since I've seen plenty of lit up badges run off one for the day, so long as they aren't at max brightness. I started looking for a battery pack on Aliexpress. I have some size constraints for the little gap between the frame and boot. The frame is 34mm wide, the height of the gap is 10mm and length about 100mm. After looking for a reasonable priced 2 pack, I found a 3.7V 703450 Lithium Polymer Battery that had the appropriate JST PH connector. It had a protection circuit, so I decided to buy it and paid $13.73 with shipping. I should get the part in a little over a week.