This is an EGO battery mount that is designed to fit in the grooves of the eBike controller included in the conversion kit I bought on Amazon (AW brand). It is based on Matt Hoover's design for the OneWheel. You can see the instructions for installing the battery terminals on that page.

It is held into place by removing the end plate on the controller, sliding the tabs between a set of "fins" on the side of the controller, and then replacing the end plate. The controller can then be mounted to a bike rack or other fixed surface. The battery should fit snugly in the mount, but I would also recommend a strap to hold the battery in place so that it does not fall out when riding over bumps.

The best way to print is to rotate it so that it is tall.

Designed with Tinkercad: https://www.tinkercad.com/things/kWSGz79Ee1i