How Do Batteries Work? A Simple Introduction - Explain That Stuff

Batteries

by Chris Woodford. Last updated: February 13, 2024.

No cellphones, laptops, or flashlights. No electric cars or robot vacuums. No quartz watches, pocket calculators, or transistor radios. And, for those of us who need a helping hand with our daily lives, no heart pacemakers, hearing aids, or electric wheelchairs.

Life without batteries would be a trip back in time, a century or two, when pretty much the only way of making portable energy was either steam power or clockwork. Batteries—handy, convenient power supplies as small as a fingernail or as big as a trunk—give us a sure and steady supply of electrical energy whenever and wherever we need it. Although we get through billions of them every year and they have a big environmental impact, we couldn't live our modern lives without them.

You might think a battery looks just about as dull as anything you've ever seen. But the minute you hook it up to something, it starts buzzing with electricity. That dull little cylinder turns into your very own micro power plant! Let's see what's going on in there...

Photo: Disposable batteries like this one are really convenient, but they can be expensive in the long haul and they're bad for the environment. A better option is to use rechargeable batteries. They cost more to begin with, but you can charge them hundreds of times—so they save an absolute fortune and help save the planet.

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Contents

1. What is a battery?
2. What are the main parts of a battery?
3. Why do batteries need two different materials?
4. How does a battery really work?
5. Types of batteries
6. Measuring batteries
7. A brief history of batteries
8. Find out more

What is a battery?

A battery is a self-contained, chemical power pack that can produce a limited amount of electrical energy wherever it's needed. Unlike normal electricity, which flows to your home through wires that start off in a power plant, a battery slowly converts chemicals packed inside it into electrical energy, typically released over a period of days, weeks, months, or even years.

The basic idea of portable power is nothing new; people have always had ways of making energy on the move. Even prehistoric humans knew how to burn wood to make fire, which is another way of producing energy (heat) from chemicals (burning releases energy using a chemical reaction called combustion). By the time of the Industrial Revolution (in the 18th and 19th centuries), we'd mastered the art of burning lumps of coal to make power, so fueling things like steam locomotives. But it can take an hour to gather enough wood to cook a meal, and a locomotive's boiler typically takes several hours to get hot enough to make steam. Batteries, by contrast, give us instant, portable energy; turn the key in your electric car and it leaps to life in seconds!

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What are the main parts of a battery?

The basic power unit inside a battery is called a cell, and it consists of three main bits. There are two electrodes (electrical terminals) and a chemical called an electrolyte in between them. For our convenience and safety, these things are usually packed inside a metal or plastic outer case. There are two more handy electrical terminals, marked with a plus (positive) and minus (negative), on the outside connected to the electrodes that are inside. The difference between a battery and a cell is simply that a battery consists of two or more cells hooked up so their power adds together.

When you connect a battery's two electrodes into a circuit (for example, when you put one in a flashlight), the electrolyte starts buzzing with activity. Slowly, the chemicals inside it are converted into other substances. Ions (atoms with too few or too many electrons) are formed from the materials in the electrodes and take part in chemical reactions with the electrolyte. At the same time, electrons march from one terminal to the other through the outer circuit, powering whatever the battery is connected to. This process continues until the electrolyte is completely transformed. At that point, the ions stop moving through the electrolyte, the electrons stop flowing through the circuit, and the battery is flat.

Why do batteries need two different materials?

"It is the difference in metals that does it."

Alessandro Volta (commenting on Galvani's experiments).

It's important to note that the electrodes in a battery are always made from two dissimilar materials (so never both from the same metal), which obviously have to be conductors of electricity. This is the key to how and why a battery works: one of the materials "likes" to give up electrons, the other likes to receive them. If both electrodes were made from the same material, that wouldn't happen and no current would flow.

To understand this, we need to delve back through the history of electricity to 1792, when Italian scientist Luigi Galvani found he could make electricity with a bit of help from a frog's leg.

Famously, Galvani stuck a couple of different metals into the leg of a dead frog and produced an electric current, which he believed was made by the frog releasing its "animal electricity." In fact, as his countryman Alessandro Volta soon realized, the important thing was that Galvani had used two different metals. In effect, the frog's body was working as the electrolyte of a battery made with two different metallic electrodes stuck into it. Dead or alive, there was nothing special about the frog; a glass jar full of the right chemicals—or even a lemon—would have worked just as well.

Artwork: Have you ever made a simple battery by pushing a zinc nail and a copper coin into a lemon? It works because these two different metals have atoms with different abilities to hold on to the electrons they contain. The zinc atoms in the nail lose their electrons (blue, e), which flow out through the circuit you've made to the copper atoms in the coin. This flow of electrons makes a current that delivers useful power, capable of lighting up a tiny bulb or LED (red). Read more about how to make a lemon battery and the chemical reactions that power it.

What was so special about the electrodes? Chemical elements differ in their ability to pull electrons toward them—or give them up to other elements that pull on them more. We call this tendency electronegativity. Stick two different metals into an electrolyte, then connect them through an outer circuit, and you get a tug-of-war going on between them. One of the metals wins out and pulls electrons from the other, through the outer circuit—and that flow of electrons from one metal to the other is how a battery powers the circuit. If the two terminals of a battery were made from the same material, there'd be no net flow of electrons and no power would ever be produced.

That's the theory anyway. Now let's look at it in practice.