3.7 V 750 mAh Li-Ion Battery for Bose QuietComfort 35 II Wireless Bluetooth Headphones QC35 and Sony WF-1000xM3 Charging Case Battery Upgrade: Amazon.de: Computer & Accessories
3.7V 400mAh LiPo AHB110520CPS battery for BOSE QuietComfort QC35 headset
Tutorial How To Repair Replace Bad Battery Bose Quietcomfort QC35 - YouTube