Looks like it may be possible to replace the battery in the new PX8 for future reference. At least going off the PX design… if you are brave enough 😆 : r/headphones
Cameron Sino 2600mAh/3400mAh Speaker Battery for Bowers & Wilkins T7 - AliExpress
Amazon.com: Bowers & Wilkins P5 Wireless Bluetooth On-Ear Headphones, Black : Electronics
B&W P5 Wireless - aptX headphones from Bowers & Wilkins