Here are two more aluminium air cell configurations. In the photo below a disc of aluminium from a can is cut out and used for the anode. Separated from it by a disc of saltwater-soaked toilet paper is an activated charcoal disc from a water filter sliced in two. On the other side of the charcoal is some copper tape (from a garden centre, normally used to keep slugs off plants). A spring clip holds it all together, and holds the terminal wires in place. This battery can provide enough power to drive a small motor. The motor draws 11mW.
The second configuration is smaller and fits in a bottle lid. A small disc of aluminium sits on top of a strip of aluminium foil in the bottom of the bottle lid. Toilet paper soaked in salt water sits above this. Half a teaspoonful of powdered activated charcoal is placed on top of the toilet paper, and a coin is placed on top of this. A spring clip holds it together and holds a wire terminal against the coin. This battery supplies 1.5mW at startup - enough to power the joule thief. The activated charcoal in this battery is homemade (a piece of pine charcoal from a camp fire).