Slide Insert for standard Milwaukee power tool battery. You'll need to add metal contact plates.
I made these for a bike light project. The tolerances are pretty tight, but it will work itself in shortly. In my implementation I cut copper sheet for the blades to connect to the battery, and made an aluminum plate for the bottom that attached to the water bottle bosses on the bike and also had a channel for a velcro strap to go around the whole assembly (bike down tube and all)
The author hasn't provided the model origin yet.