Need to add more voltage to your regular 4AA battery pack? Parallax has come up with this ingenious plug in module that adds a 5th module to your AA quad-pack holder.
This is a 9V battery pack with on/off switch and a 2.1mm barrel plug, you get both parts and will have to solder them together. Use this to battery-power your Arduino (or other electronic projects).
It's a nice quad-AA battery holder, with 6" leads.