I recently got my newest treasure, a D500 with MB-D17 grip. The camera has an EN-EL15 battery and the grip has an EN-EL15a battery. I noticed that the camera is consuming battery power from the battery in the camera even with a fully loaded battery in the grip and even while just resting in the closet in airplane mode.
I have set battery priority to grip as primary, so I am surprised that the camera battery is being used at all, but also that it is draining faster than the battery in the grip.With the camera doing nothing the camera battery went from 100 to 95% in 3 days and the grip battery from 100 to 97%.
Is this normal behavior and what can I do to keep the battery from emptying unnoticed and not have the camera ready for action?