How Everything Works
How Everything Works How Everything Works

Question 580

How does a battery work? How many different kinds of batteries are there? - BW
Batteries use chemical reactions to move electric charges from one terminal to another. A chemical reaction is a process that rearranges molecules—you begin with a certain collection of molecules and end up with a different collection of molecules. As the atoms in those molecules rearrange, they stick to one another more tightly than before and they release some of their chemical potential energy. This released energy then takes another form. While some chemical reactions such as burning will turn this released energy into thermal energy, a battery uses this released energy to move electric charges from one place to another. The battery moves extra positive charges onto its positive terminal and extra negative charges onto its negative terminal. While you can't see those charges, you can tell that they're there. If you use wires to connect the terminals to the two sides of a light bulb, the charges will rush through the wires and the light bulb will glow.

There are many types of batteries, but two of the most important modern batteries are alkaline batteries (used in flashlights and toys) and lead-acid batteries (used in automobiles). An alkaline battery uses a reaction between zinc metal and manganese dioxide to move electric charges between its two terminals. The battery's negative terminal is made of powdered zinc and its positive terminal is surrounded by manganese dioxide. Between the two terminals is an alkaline paste of potassium hydroxide. As the chemical reaction proceeds, negative charges are transferred to the battery's negative terminal and positive charges are transferred to the battery's positive terminal. As these charges are used by the flashlight or toy, the battery replaces them with new charges. Since each transfer of charges consumes some of the battery's original chemicals, the more the battery's charges are used, the more its chemicals are consumed. Eventually the powdered zinc is gone and the battery stops working. Once the powdered zinc has been used up, it can't be replaced.

A lead-acid battery uses a reaction between lead metal, lead oxide, and sulfuric acid to move electric charges. It, too, consumes its original chemicals while transferring charges. However, a lead-acid battery can be recharged easily by pushing charges through it backward. When a car is running, its generator pushes charges backward through the lead-acid battery and converts the consumed chemicals back into their original forms. This recharged battery is almost as good as new, so it can be used over and over again and lasts for several years.


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