What is a Battery?
Batteries come in various shapes and sizes and utilize a wide variety of chemicals to generate electricity. A battery is made up of one or more electrochemical cells; however, the term "battery" often is used when referring to a single cell, like the battery in a flashlight. A cell is a self-contained energy storage device that is filled with chemicals. These chemicals interact to produce electrons, and the movement of these electrons results in an electric current.

There are two different types of batteries: primary and secondary. The chemical reactions that occur in primary batteries are irreversible. As a result, these batteries discharge the energy that is stored within them once and are subsequently discarded. The chemical reactions that occur in secondary batteries, on the other hand, are reversible. These batteries are rechargeable and may be charged and discharged many times before eventually "going flat" or losing their ability to dispense power.
How a Battery Works
If a chemical reaction creates electricity, what creates a chemical reaction? The chemicals used in batteries either release electrons (oxidation) or accept electrons (reduction) readily. For a reaction to take place, a chemical that likes to donate electrons and one that likes to accept electrons need to come together and exchange particles. When this process occurs, the electrons are given a certain amount of energy, depending on the speed of the reaction. The faster the reaction, the greater the voltage produced.

Now, how do we harness the energy of these electrons? First, we need to understand the four basic elements that make up a battery: the anode, the cathode, the electrolyte and the separator. The anode is the negative electrode - or area of the battery - where electrons are lost (oxidation is occurring) and where positive ions are produced. The cathode is the positive electrode where electrons are gained (reduction is occurring) and where negative ions are produced. The electrolyte acts as a bridge between the electrodes, allowing the positive and negative ions to flow back and forth. The separator provides a reservoir for the electrolyte and electrically isolates the anode and the cathode, preventing the chemical reaction from occurring in one fell swoop.
When the anode begins to release electrons, the resulting energy must be captured so that it can be used to power a device. A connecting wire inserted between the anode and the cathode does this. As the anode releases electrons, the connecting wire catches the energy and sends it to the device. At the same time, the anode also creates positive ions, which travel into the electrolyte.
While the anode is busy donating its electrons, the cathode is busy receiving them. Just like its counterpart, the cathode also creates its own ions, which are negative. These ions move into the electrolyte as the cathode accepts electrons from the anode. This flow of electrons continues until the materials are depleted. At this point, the battery has used up all of its electrical energy and must be discarded or recharged.