How to Make a Fruit Battery

Making a battery out of fruit may sound completely ludicrous, but it is absolutely possible and is often demonstrated in chemistry classes in schools.  So long as the fruit chosen to act as the battery is a citrus fruit, meaning that it is acidic, the ability to light up a small light bulb such as a single Christmas tree light will be provided by a piece of fruit. 

In order to make a piece of fruit conduct electricity, and so act like a battery by providing an energy source, some basic equipment will be required.  Firstly, you will obviously need a piece of citric fruit such as an orange, lemon or lime.  You will also need a small light, a good example of which is a single Christmas tree light cut off a long strand of such lights with the pair of wires still attached.  The wires will need to be long enough to allow some of the plastic wire coating to be stripped back so that the wires can be wrapped around a pair of conductors.

The conductors required will need to be something like a copper screw, or nail, or even a copper coin which can be inserted into a slit made in the fruit with a knife.  You will also need a second nail or screw, as long as what you use is zinc coated or galvanized.  Nails will work best as they are generally long enough to have a large part of the nail in the fruit with enough of the nail and head sticking out of the fruit for the attachment of the wires.

To make sure that the inside of the fruit is pulped up, so that the juice is running freely, you will need to roll the piece of fruit around or squeeze it just enough to pulp the inside of the fruit without breaking the skin of the fruit.  Then the nails can be stuck into the fruit so that part of the shaft and head of the nails is protruding.  Don’t stick the nails right through the fruit, as the nails need to be immersed in the juice of the fruit.  Also, keep the nails a couple of centimetres or further apart, and avoid letting them touch in the fruit.

If you have a voltmeter, placing the positive red wire on the copper nail and the black, negative wire on the zinc nail will give a voltage reading, showing that electricity is already being produced before the wires of the light have even been connected.  As this also shows, the copper nail or coin will be the positive terminal of the battery.

With the wires of your Christmas tree light, strip back a couple of centimetres off the wire casing of each of the two wires.  Then touch the exposed ends against the nails, one wire to each of the nails to check that the positive wire is connected to the positive terminal, by seeing if the light lights up with the way you are holding the wires, reversing the wires if not.  The exposed wire of the positive wire can then be wrapped around the zinc nail shaft protruding from the fruit and either taped in place or clamped on with crocodile clips if necessary, whilst the second, negative cable is similarly wrapped around the second, copper nail. 

Once both wires are connected to the nails, the light will light up as the acid in the fruit will act as a conductor.  This works to produce power like a battery as there will be a transfer of electrons occurring within the fruit, as electrons from the zinc coated nail transfer to the copper nail and vice versa, which creates a current as the acid in the fruit works to conduct the electrons across the gap between the two nails.  The power won’t be significant as would be expected, but it may still be enough to light the light bulb.

If the light bulb won’t light up with just one piece of fruit, several can be connected with a series of wires, with the last of the positive wires with a free end attached to the positive wire of the light, and the negative wire to the negative wire of the light.

If this is being done in a school environment or as a means of education, using different acidic fruits will show how the strength of the acid within different fruits can alter the amount of electricity produced, and play around with changing the distance between the nails if the light bulb is illuminated by a single piece of fruit.