Holds 18650 battery for electronics projects. I use the positive and negative inserts linked below. The design has two holes in the bottom not just to save on filament but I use them to snap the holder into a project box. Just put two matching (but a fraction of a mm smaller) circular pads in your project box and you can snap this in once assembled.
I have used a couple different charge modules with these, linked below. See my other things for models and projects related to them.
Positive and negative battery connectors https://amzn.to/2NBT0sW