How exactly do you open the PG-81 microphone to insert the battery?
The bottom 2/3 of the PG81 unscrews from the top 1/3. The break is directly under the switch. Once un-screwed, the bottom 2/3 drops down, exposing the battery compartment.
Hold the top of the mic with one hand, and the bottom of the mic with the other. Twist in opposite directions to unscrew.