I've got a new Nikon D610, the manufacturers manual, and the book Mastering the Nikon 610, and cannot for the life of me, given a zillion googles, understand how these two things operate. I bought the MBD14 grip, have a Nikon brand LiOn battery in the camera and bought another for the grip. Where I'm confused is, do both batteries run in tandem? In other words, when I go to the battery health menu, am I seeing the health of one battery or two? If it shows a low battery, does that mean one or both are weak and need charging? If it makes any difference, both batteries are genuine Nikon EN-EL 5 batteries, which are supposed to contain a circuit that shows battery life and health. Thanks ahead for your input. J.