Sony should own up to it and offer free repairs for this design issue.
It’s very difficult to replace just the battery, so Sony offers whole unit replacement instead. It’s great when you still have warranty, not so great when you have to pay for the replacement.
Replacing just the battery is possible, see this guy doing it:
【索尼wf-1000xm4耳机更换原装电池的视频-哔哩哔哩】
https://b23.tv/xZenFeD