Here's an easy way to get lots of battery power easily. This mount uses a Makita 18v Lithium-Ion to power your projects. Shown is the 3 amp hour battery. The 1.5 amp hour battery works as well.
Search the web for the Makita Terminal, part number 6438386. It should cost about $5.00. The terminal has .250" tabs on the back for wiring.
The file Makita Battery Mount Final.stl is attached. I used a MakerBot Replicator2 at the normal settings. No raft, with supports. It should take 1.5 hours to print. The mounting holes are for #6 screws.
HAVE FUN KIDS!