Print in ABS or something else that's not brittle like PLA, because the design requires some flex to hold the battery in place. Can be resized if you know openscad. Best printed in multiples (because otherwise each layer takes such a short time that you get cooling problems). Once you've printed the shells, put a short wire with a quarter inch or so stripped off each end through the holes in top and bottom, and secure with hot glue. Works best with positive on top and negative on the bottom. And the large rectangular hole is so that you can push a battery back out.