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
Teardown, Bowers & Wilkins PX on Behance
Bowers+%26+Wilkins+B%26W+PX+B%26W+FP39691+Headphone+Ear+pad+%28single%29+ZZ34983 for sale online | eBay