How Batteries Work

Batteries have been around longer than you may think. In 1938, archaeologist Wilhelm Konig discovered some peculiar clay pots while digging at Khujut Rabu, just outside of present-day Baghdad, Iraq. The jars, which measure approximately 5 inches (12.7 centimeters) long, contained an iron rod encased in copper and dated from about 200 B.C. Tests suggested that the vessels had once been filled with an acidic substance like vinegar or wine, leading Konig to believe that these vessels were ancient batteries. Since this discovery, scholars have produced replicas of the pots that are in fact capable of producing an electric charge. These "Baghdad batteries" may have been used for religious rituals, medicinal purposes, or even electroplating.

In 1799, Italian physicist Alessandro Volta created the first battery by stacking alternating layers of zinc, brine-soaked pasteboard or cloth, and silver. This arrangement, called a voltaic pile, was not the first device to create electricity, but it was the first to emit a steady, lasting current. However, there were some drawbacks to Volta's invention. The height at which the layers could be stacked was limited because the weight of the pile would squeeze the brine out of the pasteboard or cloth. The metal discs also tended to corrode quickly, shortening the life of the battery. Despite these shortcomings, the SI unit of electromotive force is now called a volt in honor of Volta's achievement.

The next breakthrough in battery technology came in 1836 when English chemist John Frederick Daniell invented the Daniell cell. In this early battery, a copper plate was placed at the bottom of a glass jar and a copper sulfate solution was poured over the plate to half-fill the jar. Then the zinc plate was hung in the jar, and a zinc sulfate solution was added. Because copper sulfate is denser than zinc sulfate, the zinc solution floated to the top of the copper solution and surrounded the zinc plate. The wire connected to the zinc plate represented the negative terminal, while the one leading from the copper plate was the positive terminal. Obviously, this arrangement would not have functioned well in a flashlight, but for stationary applications it worked just fine. In fact, the Daniell cell was a common way to power doorbells and telephones before electrical generation was perfected.

By 1898, the Colombia Dry Cell became the first commercially available battery sold in the United States. The manufacturer, National Carbon Company, later became the Eveready Battery Company, which produces the Energizer brand.

Now that you know some of the history, click over to the next page to learn the various parts of a battery.

Take a look at any battery, and you'll notice that it has two terminals. One terminal is marked (+), or positive, while the other is marked (-), or negative. In normal flashlight batteries, like AA, C or D cell, the terminals are located on the ends. On a 9-volt or car battery, however, the terminals are situated next to each other on the top of the unit. If you connect a wire between the two terminals, the electrons will flow from the negative end to the positive end as fast as they can. This will quickly wear out the battery and can also be dangerous, particularly on larger batteries. To properly harness the electric charge produced by a battery, you must connect it to a load. The load might be something like a light bulb, a motor or an electronic circuit like a radio.

The internal workings of a battery are typically housed within a metal or plastic case. Inside this case are a cathode, which connects to the positive terminal, and an anode, which connects to the negative terminal. These components, more generally known as electrodes, occupy most of the space in a battery and are the place where the chemical reactions occur. A separator creates a barrier between the cathode and anode, preventing the electrodes from touching while allowing electrical charge to flow freely between them. The medium that allows the electric charge to flow between the cathode and anode is known as the electrolyte. Finally, the collector conducts the charge to the outside of the battery and through the load.

On the next page, we'll explore how the cathode, anode, electrolyte, separator and collector work together to produce an electrical current and keep your portable devices going strong.

A lot happens inside a battery when you pop it into your flashlight, remote control or other wire-free device. While the processes by which they produce electricity differ slightly from battery to battery, the basic idea remains the same.

When a load completes the circuit between the two terminals, the battery produces electricity through a series of electrochemical reactions between the anode, cathode and electrolyte. The anode experiences an oxidation reaction in which two or more ions (electrically charged atoms or molecules) from the electrolyte combine with the anode, producing a compound and releasing one or more electrons. At the same time, the cathode goes through a reduction reaction in which the cathode substance, ions and free electrons also combine to form compounds. While this action may sound complicated, it's actually very simple: The reaction in the anode creates electrons, and the reaction in the cathode absorbs them. The net product is electricity. The battery will continue to produce electricity until one or both of the electrodes run out of the substance necessary for the reactions to occur.

Modern batteries use a variety of chemicals to power their reactions. Common battery chemistries include:

The best way to understand these reactions is to see them for yourself. Go to the next page for some hands-on battery experiments.

A voltaic pile is an early form of electric battery. Italian physicist Alessandro Volta stacked piles of alternating metal copper and zinc discs separated by pieces of cloth or cardboard soaked in an electrolyte solution. When the metals and the electrolyte come into contact, a chemical reaction occurs, generating an electrical potential difference between the metal layers.

This potential difference allows for the flow of electric current through an external circuit connected to the pile. Volta’s piles served as a precursor to modern electrical batteries and played a crucial role in shaping the development of electrical technology and our understanding of electricity.

Luigi Galvani's Influence on Alessandro Volta

By the time Luigi Galvani started his own electrical experiments, other scientists and inventors had already delved into this area. Galvani, an Italian physician, conducted experiments that led him to further study animal electricity. He observed:

Like others, Volta believed Galvani’s theory. However, he also wanted to learn more about the connection between the metal plates and the strength of the contractions.

By 1792, about a year after Galvani’s statements, Volta disagreed with Galvani, discussing metallic electricity in publications and letters. He would later do more experiments with animal electricity. And by 1800, he had introduced the voltaic pile.

Introduction of Volta’s Piles

In the time that he spoke out against Galvani's theory and in the year 1800, there was plenty of discussion about the validity of animal electricity. In a letter to Sir Joseph Banks of the London Royal Society, he introduced the voltaic pile and discussed the electricity produced.

“The apparatus to which I allude, and which will, no doubt, astonish you, is only the assemblage of a number of good conductors of different kinds arranged in a certain matter,” he wrote. “Thirty, forty, sixty, or more pieces of copper, or rather silver, applied each to a piece of tin, or zinc, which is much better, and as many strata of water, or any other liquid which may be a better conductor, such as salt water, ley, &c., or pieces of pasteboard, skin, &c., well soaked in these liquids; such strata interposed between every pair or combination of two different metals in an alternate series, and always in the same order of these three kinds of conductors, are all that is necessary for constituting my new instrument…”

Volta’s Impact

Volta’s work contributed to the understanding of electric current and electromotive force.

He demonstrated the connection between chemical reactions and electricity, opening up new avenues of scientific exploration. English chemist William Nicholson, for example, created something similar to voltaic piles and began running experiments.

Nicholson along with Anthony Carlisle found that dipping the poles of the battery into water resulted in a chemical transformation spurred by electric energy. The discovery of water electrolysis complemented Volta’s discoveries.

Homemade Battery Experiments

If you want to learn more about the electrochemical reactions that occur in batteries, you can actually build one yourself using simple household materials.

One thing you should buy before you start is an inexpensive ($10 to $20) volt-ohm meter at your local electronics or hardware store. Make sure that the meter can read low voltages (in the one-volt range) and low currents (in the five-to-10 milliamp range). With this equipment on hand, you'll be able to see exactly how well your battery is performing.

You can create your own voltaic pile using quarters, foil, blotting paper, cider vinegar and salt.

In this experiment, the copper in the quarter is the cathode, the foil is the anode, the cider vinegar-salt solution is the electrolyte, and the blotting paper is the separator.

You can also create a homemade battery can also be made from copper wire, a paper clip and a lemon.

By now you should be well-acquainted with the basic principles by which batteries discharge electricity. Read on to discover how some batteries can be recharged.

This page was updated in conjunction with AI technology, then fact-checked and edited by a HowStuffWorks editor.

With the rise in portable devices such as laptops, cell phones, MP3 players and cordless power tools, the need for rechargeable batteries has grown substantially in recent years. Rechargeable batteries have been around since 1859, when French physicist Gaston Plante invented the lead acid cell. With a lead anode, a lead dioxide cathode and a sulfuric acid electrolyte, the Plante battery was a precursor to the modern-day car battery.

Non-rechargeable batteries, or primary cells, and rechargeable batteries, or secondary cells, produce current exactly the same way: through an electrochemical reaction involving an anode, cathode and electrolyte. In a rechargeable battery, however, the reaction is reversible. When electrical energy from an outside source is applied to a secondary cell, the negative-to-positive electron flow that occurs during discharge is reversed, and the cell's charge is restored. The most common rechargeable batteries on the market today are lithium-ion (LiOn), though nickel-metal hydride (NiMH) and nickel-cadmium (NiCd) batteries were also once very prevalent.

When it comes to rechargeable batteries, not all batteries are created equal. NiCd batteries were among the first widely available secondary cells, but they suffered from an inconvenient problem known as the memory effect. Basically, if these batteries weren't fully discharged every time they were used, they would quickly lose capacity. NiCd batteries were largely phased out in favor of NiMH batteries. These secondary cells boast a higher capacity and are only minimally affected by the memory effect, but they don't have a very good shelf life. Like NiMH batteries, LiOn batteries have a long life, but they hold a charge better, operate at higher voltages, and come in a much smaller and lighter package. Essentially all high-quality portable technology manufactured these days takes advantage of this technology. However, LiOn batteries are not currently available in standard sizes such as AAA, AA, C or D, and they're considerably more expensive than their older counterparts.

With NiCd and NiMH batteries, charging can be tricky. You must be careful not to overcharge them, as this could lead to decreased capacity. To prevent this from happening, some chargers switch to a trickle charge or simply shut off when charging is complete. NiCd and NiMH batteries also must be reconditioned, meaning you should completely discharge and recharge them again every once in a while to minimize any loss in capacity. LiOn batteries, on the other hand, have sophisticated chargers that prevent overcharging and never need to be reconditioned.

Even rechargeable batteries will eventually die, though it may take hundreds of charges before that happens. When they finally do give out, be sure to dispose of them at a recycling facility.

Next, let's take a look at battery arrangement.

In many devices that use batteries -- such as portable radios and flashlights -- you don't use just one cell at a time. You normally group them together in a serial arrangement to increase the voltage or in a parallel arrangement to increase current. The diagram shows these two arrangements.

The upper diagram shows a parallel arrangement. The four batteries in parallel will together produce the voltage of one cell, but the current they supply will be four times that of a single cell. Current is the rate at which electric charge passes through a circuit, and is measured in amperes. Batteries are rated in amp-hours, or, in the case of smaller household batteries, milliamp-hours (mAH). A typical household cell rated at 500 milliamp-hours should be able to supply 500 milliamps of current to the load for one hour. You can slice and dice the milliamp-hour rating in lots of different ways. A 500 milliamp-hour battery could also produce 5 milliamps for 100 hours, 10 milliamps for 50 hours, or, theoretically, 1,000 milliamps for 30 minutes. Generally speaking, batteries with higher amp-hour ratings have greater capacities.

The lower diagram depicts a serial arrangement. The four batteries in series will together produce the current of one cell, but the voltage they supply will be four times that of a single cell. Voltage is a measure of energy per unit charge and is measured in volts. In a battery, voltage determines how strongly electrons are pushed through a circuit, much like pressure determines how strongly water is pushed through a hose. Most AAA, AA, C and D batteries are around 1.5 volts.

Imagine the batteries shown in the diagram are rated at 1.5 volts and 500 milliamp-hours. The four batteries in parallel arrangement will produce 1.5 volts at 2,000 milliamp-hours. The four batteries arranged in a series will produce 6 volts at 500 milliamp-hours.

Battery technology has advanced dramatically since the days of the Voltaic pile. These developments are clearly reflected in our fast-paced, portable world, which is more dependent than ever on the portable power source that batteries provide. One can only imagine what the next generation of smaller, more powerful and longer-lasting batteries will bring.

For more information on batteries and related topics, check out the links on the next page.