I made this case to solve my need for a simple, small and light battery pack to power my Arduino. It holds five AAA batteries, so with NiMH(1.2v) you will get 6v or with alkaline or zinc batteries(1.5v) you will get 7.5 volts. I needed over 5v+ so I could use a Pololu 5V Step-Up/Step-Down Voltage Regulator which is more efficient then the on board regulator.
I made so a wire can be ran through the holes.
Also you can put a piece of cloth through one of the side holes to make a way to pull the batteries out.

This thing was made with Tinkercad. Edit it online https://www.tinkercad.com/things/4iphGNucmOc