Changing batteries in waterproof transmitter

Waterproof Transmitter Batteries

This case has no screws, it snaps apart & together. There is a slot in the top of the case.
Use a large flat head screwdriver in that slot and with inward pressure give a gentle twist.
That will snap apart one corner and allow the rest to be pulled apart.
Carefully pull out circuit board. There are two (CR2016) 3v button batteries on circuit board.
The black plastic retaining ring around batteries has fingernail slots to pull out. 
Use care when putting case back together that edge of rubber boot is sitting flat around edge of case to provide a good seal.