There are 2 repositories under power-bank topic.
Collection of DC/DC Converters, Battery Chargers and Power Supplies
an usb power delivery powerbank pcb based on IP5328P chip, feel free to use it
The Project explains how to build a cost-effective Power bank for mobile phones during travel and for powering up the IoT Projects as DIY (Do It Yourself)
This is an open source hardware 5V rechargeable power bank, intended for use with 1 Li-ion / Li-Pol 3.7V rechargeable battery cell.
Oitswilliam Pang 604 Multipurpose battery family.
4-lines power supply bank
Here is a system to instantaneously charge your smartphone within a SNAP⚡