The Tiny Lemon Battery, and other designs for zero cost electricity and led light without batteries

Step 10 Other designs_2: The straw battery

Basically, each cell is made up of a spiral of copper wire, another spiral of zinc-plated iron wire, inside a transparent straw filled with hand dish washing liquid, and sealed with hot glue.
Each cell generates about 0.8-1V for at least a week with a load, or 1 month and more if not used.

Then 4 of them are put in series with a led for a week of free light ;)