I call this a Gig Battery Case because I designed to bring along a set of backup batteries when I play music gigs. It holds 6 AA batteries and one 9V battery. Note that the latching nubs are on the long sides so when you open it, you need to hold it by the short sides (on the ends). Otherwise, squeezing it on the long sides will make the latches hold more strongly, and make it difficult to open.

When closed, there is a bit of extra space at the top. This is to allow the inclusion of a piece of thin, self-adhesive, insulating foam tape at the top to hold the batteries snugly. You can see it in the photo showing the open case. It's the black stuff inside the top part.