Batteries consist of two different metals suspended in an acidic solution. Copper and Zinc work well as the metals and the citric acid content of a lemon will provide the acidic solution.
Batteries like this will not be able to run a motor or energize most light bulbs. It is possible to produce a dim glow from an LED. The picture at the top of this page shows a basic lemon battery, a lemon, copper penny and zinc coated nail.
The lemon: A large, fresh, "juicy" lemon works best.
The nail: Galvanized nails are coated in zinc. I used a 2" galvanized common nail.
The penny: Any copper coin will work. (Canadian pennies from 1960 - 2001 all worked)
Creating the battery: Insert a penny into a cut on one side of the lemon. Push a galvanized nail into the other side of the lemon. The nail and penny must not touch.
This is a single cell of a battery. The zinc nail and the copper penny are called electrodes. The lemon juice is called electrolyte.
All batteries have a "+" and "-" terminal. Electric current is a flow of atomic particles called electrons. Certain materials , called conductors, allow electrons to flow through them. Most metals (copper, iron) are good conductors of electricity. Electrons will flow from the "-" electrode of a battery, through a conductor, towards the "+" electrode of a battery. Volts(voltage) is a measure of the force moving the electrons. (High voltage is dangerous!) I have connected a volt meter to our single cell lemon battery. The meter tells us this lemon battery is creating a voltage of 0.906 volts.
Unfortunately this battery will not produce enough current (flowing electrons) to light a bulb. To solve this problem we can combine battery cells to create higher voltages. Building more lemon batteries and connecting them with a metal wire from "+"