A lemon battery is a classic science experiment used to demonstrate the basics of a chemical battery system. To recreate this experiment, you will need one very juicy lemon, a galvanized (zinc-coated) steel nail, a clean copper coin (or section of household copper wiring) and a sensitive voltmeter. Voltmeters can usually be found in the electrical supply section of a hardware store, electronic hobby store or home improvement center.

The lemon battery experiment usually begins with a brief lecture on electrons and chemical reaction. The lemon contains a significant amount of acidic juice, which in scientific terminology is an electrolyte. The acid in an electrolyte helps to break down the atomic structure of the copper and zinc, causing individual electrons to be released. Carefully insert the copper coin or household copper wiring into one end of the lemon, then insert the galvanized nail into the opposite end. Make sure the two metals do not make contact with each other.

The nail and the coin have now become electrodes. Both copper and zinc allow electrons to flow through them, which means they are considered excellent conductors of electricity. The copper coin or wire is considered a positive (+)electrode, while the zinc-coated nail is a negative (-) electrode. The free-flowing electrons found in the lemon juice electrolyte naturally want to move from the negative to the positive electrodes. How fast these electrons flow is measured as voltage. The faster the flow rate, the higher the voltage will be.

A single lemon battery will not produce a significant amount of voltage, but a sensitive voltmeter should detect some electrical output. Show your audience the voltmeter's original reading of zero volts. Connect the positive clip (red casing) to the copper coin or wire and the negative clip (black casing) to the galvanized nail. The digital readout or analog dial on the voltmeter should show a small voltage number, usually less than one-tenth of a volt. This isn't enough to run a digital clock or power a lightbulb, but it does demonstrate that an electrical current can be generated through a chemical reaction alone.

Once the single-cell lemon battery demonstration is over, many instructors will ask for ideas on increasing the voltage output. This discussion may lead to the idea of a series of lemon batteries working in unison. If such a series is desired, additional wires should be attached from the positive electrode (copper) of one lemon to the negative (zinc) end of another. A series of four lemon batteries may be enough to power a small light-emitting diode (LED). Connect a negative lead to the LED wire closest to a flattened area of the casing. Connect a positive lead to the other wire and dim the room lights. There should be a dim but noticeable glow in the center of the LED. Add more lemon batteries to the series for better results.