Hi,

Here’s the Ifixit Google Pixel Buds 2 Teardown guide which shows how to open the ear buds.

The guide was only to show the internal components and is not intended as a repair guide because of the damaging way in which the earbuds have to be opened.

The battery is a Varta CP1240 A3 (supplier example only) if you think that you want to try and replace them