One of the most important issues when it comes to survival in the middle of nowhere is how to light a fire.
How to light a fire?
It turns out you won’t even really require anything too fancy to create a lemon blaze, either – some zinc and copper nails, wire, steel wool and a material that ignites are all you need.
A fascinating chemical reaction occurs after construction, and the wires are able to generate electricity. Once you touch them to the steel wool (and kindling of your choice), you’ll have yourself a nice toasty fire in seconds!
The lemon battery is a simple type of electrical battery that is commonly made for school science projects because it illustrates a battery’s main components. Typically, a piece of zinc metal and a piece of copper metal are inserted into a lemon. Everyday objects such as galvanized nails and copper pennies can be used for the zinc and for the copper. A single lemon is usually studied using an electrical meter. Several lemons can be wired together to form a more powerful battery that will power a light-emitting diode, a buzzer, or a digital clock.
The lemon battery is similar to the first electrical battery invented in 1800 by Alessandro Volta in Italy. Volta used brine (salt water) instead of lemon juice. The lemon battery is described in some textbooks in order to illustrate the chemical reactions that occur in batteries. The zinc and copper are called the electrodes of the battery, and the juice inside the lemon is called the electrolyte. There are many variations of the lemon battery that use different fruits (or liquids) as electrolytes and metals other than zinc and copper as electrodes.
There is a pretty interesting article about lemon battery on Wikipedia