This video shows how to install a 9 volt battery in the battery holder used in the Science buddies Art Bot and Brushbot projects. To view full directions for these projects, see the "Build a Brushbot" and "Art Bot: Build a Wobbly Robot Friend That Creates Art" projects at Science Buddies:
https://www.sciencebuddies.org/hands-on-activities/brushbot

https://www.sciencebuddies.org/science-fair-projects/project_ideas/Robotics_p014.shtml