The used MS-D14 AA Battery Holder from Nikon is a replacement AA battery tray for the Nikon MB-D14 Multi-Power Battery Pack.
It holds 6 AA Alkaline, Ni-MH or Lithium batteries and slides into the base of the battery pack. The MB-D14 Battery Pack is compatible with the Nikon D600 DSLR and is powered either by EN-EL15 Li-ion battery packs or by AA batteries. For each type of power source there is a separate battery holder.