Why are there so many different kinds of batteries?

This article was originally featured on The Conversation.

If you’ve looked in your utility drawer lately, you may have noticed the various shapes, sizes and types of batteries that power your electronic devices. First, there are the round, non-rechargeable button cells for your watches and small items. There’s also the popular AA and AAA cylindrical batteries for calculators, clocks and remotes. Then you have the rechargeable lithium-ion batteries in your laptops and phones. And don’t forget about the lead-acid battery in your car.

I’m a professor who studies batteries and electrochemistry. To understand why batteries come in many different sizes and shapes–and serve many purposes–look to the past, at how batteries originated and how they have developed over the years.

The first batteries were made in the 1800s, and they were quite simple. One of the first demonstrations was a series of metal discs soaked in brine, which Italian scientist Alessandro Volta found created an electric current. The first lead-acid battery was made of a few pieces of lead in a jar of sulfuric acid. The modern versions are not that different. They’re just easier to manufacture and contain various additives to improve performance.

In all cases, batteries perform in the same manner: a voltage difference between two dissimilar electrodes produces an electric current, which can be discharged to power a device. Rechargeable batteries can then reverse this current to charge back up. Inside the battery, the electric current is accompanied by the flow of ions through a liquid, the electrolyte.

The passage of each electron in the current is accompanied by the transport of one ion through the electrolyte. Electrodes that can store more ions lead to batteries that can hold more charge and therefore last longer on a single charge. Electrodes that are engineered for faster ion storage lead to batteries that can discharge faster, for high-power applications. Lastly, being able to charge and discharge many times without degrading leads to batteries with long lifetimes.

Lead-acid batteries

The lead-acid battery was the first rechargeable battery invented back in 1859 by Gaston Plante, who experimented with lead plates in an acidic solution and found that the flow and storage of electric current could be reversed.

A lead-acid battery has to be big enough to provide enough charge to start a car. It also has to be usable in cold climates and last many years. Since the electrolyte is a corrosive acid, the external casing has to be tough to protect people and car parts from any possible harm. Knowing all this, it makes sense that modern lead-acid batteries are blocky and heavy.

Alkaline batteries

On the other hand, household devices like calculators and digital scales can afford to use smaller batteries because they don’t require a lot of charge. These are primarily non-rechargeable alkaline batteries that have been used for decades. The standardized cell sizes are AAAA, AAA, AA, C and D, as well as button and coin cells and many others. The sizes are related to how much charge they store – the bigger the battery, the more it holds–and the sizes of the devices they power.

Sometimes, you may find alkaline batteries sold in rectangular shapes, like common 9-volt batteries, but open the outer casing and you’ll find that they are simply a few cylindrical cells connected together inside. Cylindrical batteries have been around so long and used so widely that it just doesn’t make sense for the companies to manufacture anything different–it would require an investment to change their manufacturing facilities, something they’d rather not do.

Why are there so many different kinds of batteries?

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