I bought a too-big battery for my SonarMote kit. I designed this box to hold the SonarMote and my battery. I used OpenSCAD, so the box dimensions can be adjusted to fit your battery.
https://www.thingiverse.com/thing:4183689 (https://www.thingiverse.com/thing:4183689)
Very cool, thanks for sharing, I added a link on the SonarMote guide (https://lowpowerlab.com/guide/sonarmote/) ;)