The target of this design is to provide power supply and backup energy for Raspberry Pi. It was designed in the format of Raspberry Pi Zero to build a stackable complex in the end.

You can see the PSU board above Raspberry Pi 3B+ in the following picture:

and the same assembly with connected battery to the PSU board:

I used a cheap LiIon battery charger + DC-DC step up booster from AliExpress for battery management as well as for voltage conversion to 5.1V on its output. It works flawlessly. Don't forget to set appropriate voltage before soldering the module!

The schematics of Power Supply Unit:

PCB layout:

The PCB design files in Gerber format and BOM were exported from KiCad and are downloadable here:

RPi_PSU_Gerber.zip

RPi_PSU_BOM.pdf

I also created an installing script for Raspberry Pi to monitor buttons and battery low voltage of the connected board. Just run it from the command line.

RPi_PSU_PwrCtrl.sh