Adafruit 9V Battery Case w/ Switch and Barrel Connector - RobotShop
The Best Cheap 9V Rechargeable Battery 600mAh for sale – EBLOfficial
L522BP2 - Energizer - Battery, 9 V, PP3
Amazon.com: Rechargeable 9V Smart Batteries with USB Charger by Pale Blue, Lithium Ion 9 Volt 500 mAh, Charges Under 1 Hour, Over 1000 Cycles, 2-in-1 USB to USB-C Charging Cable, LED Charge