Electric battery

An electric battery is a source of electric power made up of one or more electrochemical cells. These cells have positive and negative parts called terminals. When a battery powers something, like a flashlight, electrons flow from the negative terminal through the device and back to the positive terminal. This flow of electrons is what makes things work, and it involves a special kind of chemical reaction called a redox reaction.

There are two main types of batteries. Primary batteries, like the small ones used in remote controls or toys, can only be used once and then thrown away. But secondary (rechargeable) batteries, such as those in smartphones or cars, can be plugged in and used again many times. When you recharge a battery, you send electricity back through it, which resets the chemicals inside.

Batteries come in all kinds of sizes and shapes. Some are tiny, like the ones in your hearing aid or watch, while others are huge, big enough to fill a room and keep important places like phone systems running during power outages. Even though batteries don’t store as much energy as fuels like gasoline, they are very efficient at turning stored energy into power that makes things move or work.

History

Main article: History of the battery

The idea of using electricity stored in devices began with Benjamin Franklin, who called a group of special jars a "battery" in 1749. Much later, in 1800, Alessandro Volta created the first true battery, called the voltaic pile. It was made of layers of copper and zinc with paper soaked in a salty liquid in between, and it could provide a steady flow of electricity.

Over time, scientists improved batteries so they could be used in many everyday devices. Today, batteries are very important for powering cars, homes, and even helping to manage electricity on power grids. Researchers are always finding new ways to make better batteries.

Chemistry and principles

Main articles: Electrochemical cell and Voltaic cell

Batteries change chemical energy into electrical energy. They do this by using special reactions between metals, oxides, or molecules. For example, metals like zinc or lithium can store a lot of energy because they are not stabilized by certain types of bonding.

A battery is made up of one or more voltaic cells. Each cell has two parts called half-cells, which are connected by a special liquid called an electrolyte. This electrolyte helps move tiny particles called ions between the two half-cells. One half-cell has the negative electrode, and the other has the positive electrode. When the battery is used, it creates a force called voltage that pushes electricity through a circuit.

Types

See also: Battery nomenclature and List of battery types

Batteries can be grouped into two main types: primary and secondary. Primary batteries are used until their energy runs out, and then they are thrown away. They cannot be recharged because their chemical reactions are not reversible. Secondary batteries, also called rechargeable batteries, can be recharged many times. When you charge a rechargeable battery, you reverse the chemical reactions that happen when it’s used, bringing it back to its original state.

Some common primary batteries include zinc–carbon and alkaline batteries, often used in flashlights or remote controls. Rechargeable batteries, like lead–acid, nickel–cadmium, nickel–metal hydride, and lithium-ion, are used in cars, computers, and many portable devices. Each type has its own advantages, such as how much energy it can store or how long it lasts before needing a charge.

Performance, capacity and discharge

See also: State of charge, Depth of discharge, and Trickle charging

A battery’s performance can change depending on factors like temperature and how much power is being drawn from it. In cold weather, batteries don’t work as well, which is why some people use special heaters to keep car batteries warm.

The capacity of a battery is how much electric charge it can provide before its voltage drops too low. Bigger batteries have more capacity than smaller ones, even if they are made of the same materials. Capacity is usually measured in ampere-hours (A·h). For example, a 100 A·h battery can provide 5 A of current for 20 hours at normal room temperature. However, if you draw power faster, the battery will last for a shorter time.

Batteries also lose charge over time even when they’re not being used, due to natural chemical reactions inside them. This is called self-discharge. When batteries are recharged many times, their capacity can decrease until they no longer work well. How quickly a battery charges or discharges is described by its C-rate. A lower C-rate means the battery can provide more of its capacity over a longer time, while a higher C-rate allows faster charging but reduces the battery’s overall lifespan. Recent advances have led to experimental batteries that can charge very quickly, such as prototypes that can reach 80% charge in just a few minutes.

Lifespan and endurance

Battery life means how long a battery can power a device or how many times it can be recharged before it stops working well. For non-rechargeable batteries, like the ones in remote controls, life is just how long they can run before the power runs out. For rechargeable batteries, like those in smartphones, life also means how many times you can charge and use them before they wear out.

Some batteries, like the very old Zamboni pile, can last a very long time without needing to be recharged, but they don’t give much power. Most batteries lose a little bit of their power each year just sitting on a shelf—this is called “self-discharge.” Storing batteries in a cool place can help them last longer, but they should be brought back to room temperature before use. Different types of batteries last different amounts of time, with some lasting thousands of charges before they need to be replaced.

Hazards

See also: Lithium-ion battery § Safety, and Battery leakage

Batteries can be dangerous if not handled properly. They can sometimes explode if they are misused, such as trying to recharge a battery that cannot be recharged or creating a short circuit. This can happen if a battery is charged too quickly, causing gases to build up inside and eventually burst the battery case. Car batteries can also explode if they are overcharged, producing explosive hydrogen gas.

If a battery leaks, the chemicals inside can be harmful. It is important to dispose of batteries correctly to avoid harming the environment, as many contain toxic materials. Batteries should never be swallowed, especially small button cells, as they can cause serious damage inside the body.

Legislation and regulation

Laws about electric batteries focus on safe disposal and recycling. Because of some accidents, like explosions, more devices with lithium-ion batteries are sometimes recalled.

In the United States, a law from 1996 stopped the sale of batteries that contain mercury and made rules for labeling rechargeable batteries. Some places, like California and New York City, do not allow people to throw away rechargeable batteries as regular trash. Recycling programs for these batteries exist across the country.

In the European Union, similar rules require more recycling of batteries and research into better ways to recycle them. Batteries sold in the EU must show a special symbol to remind people to recycle them. Starting in 2026, new rules will require that batteries in many devices can be easily removed and replaced by consumers.