Amazon.com : Rechargeable Li-ion Battery for Nikon EN-EL15 and Nikon D600, D610, D800, D800E, D7000, D7100 Digital SLR Camera and Nikon 1 V1 Digital Camera : Electronics
Nikon MB-D14 Multi Battery Power Pack 27065 B&H Photo Video
Meike MK-D600 is a cheap alternative battery grip for Nikon D600 - Nikon Rumors