Solder three header pins into the charging backpack.
Take a utility knife and break the trace between the two connected pins next to the header. This will enable you to add an on/off switch to the fans.
Trim the wires on your on/off switch so that one is slightly longer than the other, and both wires are about 3/4" long. Solder one wire to each of the switch pins on the charger board so the switch sticks out at about 90 degrees.
Solder the three header pins into the first three pins next to the USB port on the Trinket (BAT, G, 5v).
Plug your battery in to the JST connector and click the switch. You should see some blinky lights come on. It's ALIVE! Muahahahah...
LEDs & Mode Switch
Unplug the battery and be sure it's unplugged for all the rest of the soldering.
Place the Pro Trinket into the enclosure and thread all four LED wires through the wire slot. Starting with the power and ground wire, measure about how long they need to be and solder them onto the back of the Pro Trinket.
Place the Pro Trinket back in its little spot and do the same with the Data (pin 3) and Clock (pin 4) wires. Solder them in place.
Solder a 6" wire to pin 5 and to the GND pin on the Pro Trinket. These wires will go to your mode switch.
Cut off both legs on one side of your momentary switch. Carefully bend the other two legs out so your switch can sit flat on the table.
Place the Pro Trinket back in your 3D printed enclosure and feed the switch wires out through the slot on the battery side. Trim them to a comfortable length for reaching the switch with your thumb while holding the fan by the handle.
Slip some heat shrink tubing on to both wires and solder them securely to the remaining legs on the switch, and secure them with heat shrink.
Place the switch along the narrow edge of the plastic where it's comfortable to reach with your thumb while holding the fans. Hot glue it in place. Feel free to be generous with the hot glue so it stays, but be careful not to get any on the working part of the switch.
Plug the battery in and pop the lid onto the enclosure with the on/off switch positioned inside the hole.
We will glue all this in place later, but for now, let's upload some code and make sure it works!