Like socks, battery covers tend to disappear without explanation. It happens.
This particular battery cover is for a Neiko Caliper. Specifically, this one.
I personally didn't want this to come out of the caliper without a significant, and intentional effort on my part, so I designed it to be quite tight. That said, you may need to tweak the dimensions slightly for it to fit how you like.
Also, you'll probably want to print this upside down (the outside edge facing the print bed), but that's entirely up to you.
I designed this with a .10 resolution in mind. This makes the grooves just the right size to fit snugly into the case. If you change that around, you may need to tweak the model a bit.