Well the battery died quite some time ago, but well out of warranty, and it was left to find a moment when a repair process could be enacted, a replacement battery be found and a resurrection be performed. Today was such a day.

The repair process

A search found that Maurice Brg, among others, had not so long ago performed such an operation. The difference between him and others is that he prepared a report on the matter:
https://mauricebrg.com/2024/05/sennheiser-pxc-550-battery-replacement.html
A very thoughtful man who recognises that if you have a question others will have the same question but do not dare to ask it. So he did, and he provided the answer as well.

Coco could not describe it better. Not only did his repair succeed, he knows what technical terms like spudger mean, not that you need to know the technical terms because his description is in plain easy to read English.

If your PCX550 requires some TLC in the form of a new battery, you could not visit a more helpful place that Borgmeier’s Blog.

Footnote: Coco has only completed the first part of the operation. There was no point, he thought, to acquire a battery if he could not open the baffle.