Greetings to all: I want to purchase a GX 680 and was wondering if the batteries in the film back power anything other than the LED? I would assume that the battery pack in the camera runs the motor, meter, etc. I also understand that the batteries in the back are not easily replaced. If all they power is the LED, then one could, I presume, continue using the back. Any information and/or comments would be most welcome. Thanks in advance for your help.