This cell is made from the base of an aluminium soft drinks can, a disc of tissue paper soaked in saturated salt solution, and an activated charcoal disc for a water filter. The image below shows these components.
The charcoal disc is soaked in salt solution for 10 minutes before assembling the battery. The tissue paper is placed over the can base, then a few drops of salt water solution are dripped onto it, as shown below.
The two thin fibrous membranes attached to the charcoal disc are peeled off, then the disc is inserted into the hole in the can base. Coincidentally, it is a snug fit. Take care not to tear the tissue paper.
The can base serves as the negative terminal of the cell. The positive terminal is a coin and piece of wire pressed against the charcoal disc by a spring clip, as shown below.