We designed these 3D-printed Battery Holders for both Rev and Tetrix batteries. They were designed in solidworks and you can download the print file at this link: (for Rev: https://www.thingiverse.com/thing:2794588) (for Tetrix: https://www.thingiverse.com/thing:2794818)
This is the Rev Battery Holder:
Tetrix Battery Holder:
Trial and Error 10191 