I decided to 3D print a case for an Al-air cell. The diameter of the case is just large enough to hold a charcoal water filter disc. Ideally I would use a thinner disc, but the size that I am using happens to be available cheaply. The photos below show how the battery is put together. Note that the photos show two 12mm M3 bolts, but I ended up using 20mm bolts, not 12mm. The bendy wire shown in the photos is lead free solder with a tin content of 99.3%, chosen because it is unreactive. I used aluminium foil folded over four times and cut into a disc shape as the energy source. In the fourth step, 4 drops of saturated salt water solution are dropped onto the tissue paper.

After it was assembled, the cell produced 12mW when powering a joule thief, as shown below: