The Nikon MS-D12 AA Battery Holder for MB-D12 Multi-Power Battery Pack allows users of the Nikon D800, D800E, and D810 digital cameras with the MB-D12 Multi-Power Battery Pack to use 8 AA batteries instead of the Nikon EN-EL15 lithium-ion battery. This is especially useful when shooting in cold weather. Also, you can keep an additional MS-D12 AA battery holder pre-loaded, so that you can quickly swap out battery sets.
Anyone that's spent time in Nikon's ecosystem has experienced their monomaniacal hatred of third-party accessories. You never know when a firmware update is going to include undocumented payload that will break your battery eliminator. Meanwhile, there isn't even a first-party solution available since Nikon's EP-5b eschews standard DC connectors for something proprietary that only mates with their AC power bricks. I needed a way to power my camera from an external DC source and I settled on modifying this insert since I already owned the battery grip. It allows the camera to be powered from 8 AA batteries. Support for NiMH, alkaline, and primary lithium batteries translates to an input voltage in the range of 9.6V-12.4V that's easy to satisfy. This adapter gives easy access to two large solder pads that are connected to the positive and negative ends of the eight series batteries. With a very basic soldering capability, you can desolder the battery contacts and connect wires from your input jack of choice. The camera has no way of telling the difference between AA batteries and any other battery type that can produce the expected voltage. As you can see in the picture, this results in a clean appearance and a DC input that is out of the way of both the horizontal and vertical grips. When you want to go back to internal power, you can switch battery grip inserts in a matter of seconds. I'm using a 12V regulator to feed power from an external V-mount battery, which the camera shows as a full pack of AA batteries.
This holder holds 8 AA batteries. Nikons MB-D12 battery grip holds only one EN-EL15 battery, plus the one in the camera body, so thats a total of only two batteries. I just bought a new camera, a Nikon D800E, which has a larger buffer than my old camera, and Ive been working with models, so I cant tell you exactly how many frames I need to shoot. If Im shooting RAW or TIFF formats, Its possible that I could deplete two EN-EL15s before Im done, but with 8 rechargeable NIMH AA batteries, Im pretty confident I wont run out of power before the session is over. However, this setup with the D800E, the MB-D12 battery grip, and 8 AA batteries, is pretty heavy, so I dont recommend this for everyone. I use a monopod for extra sharpness (Im shooting 36.3MP), so that takes the heavy load off my wrists and hands. That extra weight provides a lot of stability, but its hard to hold for a long time without some sort of support.