What is a battery?

A battery stores energy in a form that we can use to power all of the electronics around us.

What? That’s not an answer! How? Why? Is it magic?

Batteries are divided into two halves: a positively charged half and a negatively charged half. The positively charged half is full of particles with a positive charge, and the negative half is full of particles with a negative charge.

If we were to imagine a battery as a Shakespearean play, positively charged particles are Juliet’s and negatively charged particles their Romeo’s. A battery works by separating Romeo’s from Juliet’s. The pairs will do anything to be together, so that gives the battery potential energy.

Crude drawing of battery separated into positive and negative halves.

So a fully charged battery has a bunch of positive things on one side and a bunch of negative things on the other side. They want to be friends, but the battery won’t let them. Got it.

But then, how does a battery power the computer I am typing on?

When a battery is not connected to an electronic device, there is no way for the Romeo’s and Juliet’s to be together. But, let’s say we connect a phone to the battery. Now there is a path from Romeo to Juliet, but it goes through the phone.

Battery connected to a phone. Romeo’s are streaming through the phone and powering the phone on the way.

Romeo being Romeo, will fight to get to Juliet, but to get there Romeo will have to travel through the phone. And the phone will say, “hey Romeo, I’ll let you through, but you’ll have to do some work for me.” And Romeo will then be used to power the phones screen, run an app on the phone, anything on the phone that requires electricity.

Samsung’s Note 7 explosions can also be explained with this metaphor. With the Note 7, Samsung was trying to push the limit with battery capacity. They did this by squishing together Romeo’s and Juliet’s. So at a certain point, under a lot of pressure, the Romeo’s have enough power and energy to overwhelm the separator. At that point we have a full on medieval war, and the battery heats up and explodes.

Damn, I never knew Shakespeare would still be relevant.

How have batteries changed over time? Is the big battery sitting in my car the same kind of battery that is in my phone?

All batteries have the same general structure of a positive half, a negative half, and something separating the two halves. Batteries of different types differ on what chemicals they use for the different components.

The voltaic pile — the world’s first battery!

The voltaic pile is commonly thought of as the first battery. This pile was invented by Alessandro Volta at the end of the 18th century. The voltaic pile uses Copper for Juliet, Zinc for Romeo, and cardboard to separate the two. The physics community was so happy with Volta’s battery that they named the unit for electric potential, the Volt. Good work, Alessandro!

The battery in your car is a lead-acid battery. Lead-acid batteries have two different types of lead separated by sulfuric acid. These batteries are good at holding a charge in a wide temperature range and can provide a lot of power for a short period of time. Thus, these batteries are perfect to start your car.

Today, almost all of the batteries in portable electronics use Lithium-ion batteries. The positive half uses lithium, the negative half uses graphite, and a form of carbon is often used as the separator. Lithium-ion batteries are cheap, light, high capacity, and have a ton of other benefits that we will detail in another post.


Hopefully this high-level overview helps you understand what a battery is and how it works. Comment below if you have any questions.

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