AAA Battery Pack for Xbox 360 Controller. Instead of AA batteries, you can put AAA batteries into your controller.

AAA battery mod was modeled by MikeTheMan32 and GTRsdk

Printed using 0.3mm layer height and 10% infill on a Printrbot Simple Maker's.
You then put a small piece of aluminum foil between the top groove where the batteries will make contact with, insert the batteries (paying attention to the + and -), and insert into a controller.

For our test model, we didn't even need any tape or glue for everything to stick in well.