Nikon MB-D14 Multi-Power Battery Pack for Nikon D600/D610

How can there be $170 difference of cost for an extra battery connection? vs the $50 versions out there (Honest enquiry)

This work in the Nikon D610?

How can you tell if you geat a counterfiet verson of this grip?

Two battery. How does it hold two? And what happened to one be changed?