Nikon VG-D70 Manual
Battery Packs
The VG_D70 can operate with one or two battery packs installed. It doesn’t matter if one of the battery packs is not charged. The grip will automatically use the battery with the greater charge.
If two battery packs are desired, simply drop one into the bottom of the grip, so that the battery pack’s metal contacts will touch the exposed springs in the grip. If you install this battery pack incorrectly, nothing will be damaged, but this battery won’t be connected.
If you use one or two packs, one must be placed upright on the grip, and the tethered battery cap dropped over the end of the battery pack. There are contacts in the cap which mate with the battery pack, and the orientation becomes obvious when you handle it.