This is a guide on printing your own Xbox 360 battery pack. There are many other DIY Xbox 360 battery packs online using AA batteries. However, this one allows the batteries to be changed easily and incorporates a clip to ensure it doesn't fall out of the controller.

Supplies

Aluminium Foil
3D Printer
Scissors
Small flathead screwdriver (or other support removal implement)
2 x AA batteries

Step 1: 3D Printing

Load the attached .stl file into your slicer of choice. I have a Creality Ender 3 Pro 3D printer and will use the default Creality slicer.
Ensure the battery holder is on its side as pictured. Otherwise, the clip will not bend.
Make the following changes to your default printer settings
Density = 10%
Wall thickness = 2 layers
Enable auto-generation of supports

Step 2: Removal of Supports

Most of the supports are easy to remove. The hard supports to remove are the ones around the clip. Look at the 3D model in the slicer software to ensure you know where all the supports are. Removing the supports around the clip will take more than a couple of minutes.

Step 3: Aluminium Foil Connector

Fold the foil 4 times into a strip with a width equal to the battery diameter.
Cut the strip away from the rest of the foil. The length of the strip can be 5-10cm.
Twist the strip in the middle.
Cut the strip to the size of the battery pack battery slot.
Place the strip in the bottom of the battery pack slot.

Step 4: Using the Battery Pack

Insert the battery pack batteries first as pictured and ensure the battery terminals are touching the springs.
To remove the battery pack, push the button on the clip and pull it out.