Ultra-Thin LiPo Battery - 0.1mm thickness you can find here
Lithium Ion Polymer Battery - 3.7V 350mAh : ID 2750 : $6.95 : Adafruit Industries, Unique & fun DIY electronics and kits
LiPO Batteries: Filament Power Batteries - Ultra Thin LiPO & Standard – Upgrade Keyboards
Amazon.com: ACCTN XinlanTech 1800mAh Replacement Battery for Sony PS4 Pro Slim Cuh-zct2u Cuh-zct2e Controller and Playstation 5 Pulse 3D Headset Battery Replacement : Video Games