This is a snap fit case to build a USB power bank using a soldering iron and the required parts (sourced from Aliexpress). A off-the-shelf battery holder is used to make it easy to build. You can easily make your own battery holder if you prefer.
 

The USB board supports 5V/2A Input or Output with LED indicators to show battery remaining.

USB-A port for power out. (eg. charging your phone)

USB-C port for charging (power-in) the power bank.

Parts needed:

• 1x USB charging board (weld USB option): https://www.aliexpress.com/item/1005001589184111.html?spm=a2g0o.order_list.order_list_main.15.5ff11802umM3Aq
• 1x 18650 SMD/SMT Battery Holder: https://www.aliexpress.com/item/32831937650.html?spm=a2g0o.order_list.order_list_main.9.5ff11802umM3Aq
• 1x 18650 Lithium Ion battery (3.7/3.8V) of your choosing.
• 22AWG gauge (or wire rated to carry up to 5 amps) insulated wire in red/black colour

Tools needed:

Soldering iron kit

Instructions:

1. Cut 110mm of red 22AWG wire. This will be the positive terminal wire.
   Cut 30mm of black 22AWG wire. This is the negative terminal wire.
2. Before putting the parts into the case, solder the red/black wires from the battery holder to the USB board.
3. Fit the parts (USB board & battery holder joined by soldered cable) into the case, by first slotting in the USB board into the front cut-out. Then push down firmly until the USB board is held in place and the USB ports are oriented correctly. Make sure the battery holder is seated in the case. You can add adhesive or blu-tac to secure it to the case.
4. Insert 18650 battery cell (ENSURE CORRECT POLARITY!)
5. Add thermal paste on top of the board and install the heatsink.
6. Before using the power bank for the first time after battery connection, you need to plug in the charger for at least 10 seconds to activate the USB board.

Battery indicator

The battery indicator on the side is still being worked on. For now it is a wide opening to accommodate printer/usb board tolerances so that you can actually see the LED indicators.

Print Settings:

It is possible to print without support, the bridges will bend slightly, but I have accounted for this in the model so that it should still work fine. You may require a well calibrated printer to get the snap fit case to work properly.

Layer Height: 0.10 to 0.20mm (Usually printing 0.20mm will be fine, but the snap fit areas of the case/lid may be better if printed at around 0.10mm)

Nozzle size: 0.4mm

Supports: Not required

Material: PETG (recommended), PLA (this works, but prolonged use of power bank can result in the case deforming)