AAA to AA battery adaptor

This thing is a sleeve for AAA batteries so they can be used in devices requiring AA batteries. You also need a small amount of Aluminium foil or similar to scrunch up and shove in the bottom to form the contact.
I have portable phones that are always on charge around the house, and my kids always use the AA batteries without ever recharging them, so this way I can simply put flat AAA's into a phone and use the charged ones in my AA devices.