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The Role of a Battery:
The role of a battery (or cell) in an electric circuit is to supply energy to the circuit by doing work upon the charge to move it from the low energy terminal to the high energy terminal. By moving charge to high energy, the battery (or cell) is establishing a difference in electric potential across the two ends of the external circuit. With this difference in electric potential established, charge will spontaneously flow through the external circuit.
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Some students of physics have the incorrect conception that a battery's role is to supply the charge that moves through a circuit. Their thought is that when a battery no longer works, it is out of charge. After all, the battery must be recharged to work again. But don't be fooled! Batteries do not supply charge to a circuit. And the use of the phrases rechargeable and recharged are unfortunate misnomers. A battery is actually being re-energized rather than recharged. It's energy-producing ability are being restored by the reversing of the chemical reaction that occurs inside. See Think About It section.
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The battery's role in a circuit is all about doing work and providing energy. It supplies this energy by means of an electrochemical reaction that establishes an electric potential difference between the two terminals of the battery. The chemical reaction involves reactants and products. The reactants become used up over the course of time and the products get in the way if they remain bound inside the battery (or cell). Certain battery types are said to be rechargeable. That is, the reaction that typically runs to produce products can be reversed. Reversing the reaction requires an external energy source to cause the reaction to run in the reverse direction. By reversing the reaction, products can be reformulated into reactants and the ability of the cell to produce energy is restored.
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