make sure not to confuse the battery door with the audio cable cavity. when the audio cable is removed, there is a noticeable cavity at the bottom of the left earcup. this may be confused with the battery compartment at the top of the right earcup. be careful opening and closing the battery compartment door; it is not a replaceable part.
My battery door is missing.
Note: When the earcup is folded flat for storage, the battery door is obscured by the headband yoke.