Running a Raspberry Pi from 6 AA Batteries - Raspberry Pi Spy
Powering a raspberry pi from battery – Tobias Weis
Powering the Raspberry PI Pico from External Batteries
Amazon.com: MakerFocus Raspberry Pi 4 Battery Pack UPS, RPI Pack Standard 4000mAh Raspberry Pi Battery USB Pack Raspberry Pi Latest Version V3Plus Expansion Board Power Supply Type-C for RPI 4B 3B+ 3B