A guy has managed to make potato battery which can power a small sound system. Each potato generates 0.5 volts and 0.2 milliamperes of power. To increase the voltage, groups of potatoes are connected together in series and these groups are connected together in parallel to increase the amperage. The guy attached 500 lb of Potatoes to generate 5 volts and 4 milliamperes of power.
Batteries work by allowing electrons to pass from one electrode to another. In this case the potato provides phosphoric acid, which enables a chemical reaction causing electrons flow from copper to zinc. The zinc came from galvanized nails and copper came from small pieces of copper. You don’t have to use potatoes; any acidic medium such as citrus fruit will work. I chose potatoes because they are traditional and cheap.