Do not try this at home. A simple way to destroy all devices.
Parts used in this video:
Contacts: https://www.aliexpress.com/item/10050...
Batteries Holder: https://www.aliexpress.com/item/33053...
Batteries: https://www.aliexpress.com/item/10050...
Powerbank PCB #1: https://www.aliexpress.com/item/40007...
Powerbank PCB #2: https://www.aliexpress.com/item/10050...
Powerbank PCB #3: https://www.aliexpress.com/item/10050...
Powerbank PCB #4: https://www.aliexpress.com/item/10050...
Files for 3D printer here: https://www.thingiverse.com/thing:605...
or here: https://www.printables.com/model/4955...