Pinhole on the back of Eufy Doorbell

Hi,

Does anyone know what this pinhole on the back of my Eufy 2k Doorbell is? I tough this was a reset button, soo put the pin tool there. And I think some membrane punctured in there.

Anyone?

Having looked at a teardown of the battery doorbell online I think it would have punctured the plastic that holds the 2 cells of the battery together (but not the batteries themselves)