Quote Originally Posted by flatulent1 View Post
Mamiya 645 Pro TL has a circular switch around the shutter button on the body. The power grip also has a switch around its shutter button. I keep forgetting to turn one of them off, and I don't know which is necessary to keep the batteries from dying.

You probably need to lock both switches in order to prevent either one of them from being accidentally pressed when the camera is being handled or stored.

Otherwise, the camera itself prevents battery drain, by "timing out" automatically after a set period of time.