D5200 Battery Grip Question

Hi guys! This is my first post

I have a question.. I've acquired a Nikon D5200, and bought a battery grip (Meike MK-D5200).. I have 2 batteries installed. What i would like to know is, does it run both batteries simultaneously, or does it drain one and then switches to the other?

I think it drains one then the other. But not having that grip, I can't say for sure.

I got the xphoto and i think it does one at a time