Tiny nugget I found interesting:

We got around to opening up the 40 mm model and noticed a significantly different battery. This one has a snazzy new metal casing, as well as 10% more battery capacity than the Series 4 40 mm model. We’re going to spend some time researching and trying to figure it out. If nothing else, it seems to provide a tougher outer shell that is more resistant to pry damage. We doubt that’s its primary purpose, but we’re rummaging through patent filings for clues.

Always amazed at how much tech can fit in such a tiny enclosure. Even more so with AirPods.