With the battery pack removed from the earpiece surround, you can work on the battery pack disassembly.

Start by gently prying back the red tangs of the red sleeve and pushing the battery pack out of the housing. The read sleeve will slide off as well as a black silicone sleve.

To remove the PCB from the battery, carefully cut the double sided tape underneath the board on the side away from the soldered joint.

Once you are close enough to the solder joint and board is flexing a little, desolder while gently prying the board up and away. This may take several heat and flex cycles to fully pull it away. Repeat this process for the other side.

By this point, the PCB should be free of the battery.