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How Does A Car Battery Work?

A car battery. A car battery may not seem like an important component in your engine bay, but they're complicated energy storage devices that are responsible for a crucial chemical reaction.

Car batteries have been in use just over a century, working in silence under the hood or in the trunk of vehicles around the world. We usually don’t pay much attention to the car battery unless something stops working, but how does a car battery work in the first place?

A car battery is an energy storage device based on scientific discoveries made in the late 1700s, culminating with Alessandro Volta creating the first true battery in 1800. Volta’s battery consisted of dissimilar metal plates separated by cloth sheets soaked in brine, an electrolyte solution. Volta couldn’t fully explain how this delivered a slight electrical charge, but others built on his work, continually improving the technology.

What's Inside a Car Battery?A car battery’s exterior is a heavy plastic box with a couple of terminals that connect to the vehicle. Things are more interesting inside, where there are six partitioned cells. In each cell, metal plates are interleaved with insulating sheets and submerged in acid. Every other plate connects in parallel within the cell, in series with the other cells. Each cell generates 2.1 V, connected in series for a total of 12.6 V.

How Does a Car Battery Work to Deliver Energy?

What exactly does this arrangement do to deliver energy to the starter motor, radio or headlights? The secret is in how the metals react to the acid. Lead plates (Pb) and lead oxide (PbO2) plates are immersed in sulfuric acid (H2SO4). Both plates react with the electrolyte to form lead sulfate (PbSO4), water (H2O) and extra electrons, which collect on the negative terminal of the battery.

Pb + PbO2 + H2SO4 → PbSO4 + H2O + 2e

Disconnected, the chemical reaction can’t continue because the electrons have nowhere to go. Connected, a car battery delivers a lot of energy very quickly. Even at freezing temperatures — sulfuric acid doesn’t freeze — a 600 CCA car battery can deliver enough power to start a V8 engine.

How Does a Car Battery Store Energy?

Volta’s and later batteries, at least until the mid-1800s, suffered a serious flaw — they could only deliver energy until the metals were completely corroded, at which point they had to be discarded or rebuilt, just like the AAA and AA batteries (cells, really) powering your flashlight. The first lead-acid battery, invented by Gaston Planté in 1859, changed everything.

Once that quick burst of energy starts the engine, the generator starts feeding electrons back into the battery. Unlike Volta’s zinc-copper-brine battery, Planté’s lead-lead-oxide-sulfuric-acid battery easily reverses the chemical reaction. The extra electrons are forced out of the plates, recombining lead sulfate and water into lead and sulfuric acid, ready to deliver electricity on demand.

Car battery technology may be a century old, but it’s so reliable, economical and easy to recycle that a suitable replacement has yet to be found. Don’t forget to recycle your old car battery to prevent environmental contamination and to help make new car batteries.

Check out all the car batteries available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on how a car battery works, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo courtesy of Pixabay.


Benjamin Jerew View All

Ben has been taking things apart since he was 5, and putting them back together again since he was 8. After dabbling in DIY repairs at home and on the farm, he found his calling in the CGCC Automobile Repair program. After he held his ASE CMAT for 10 years, Ben decided he needed a change. Now, he writes on automotive topics across the web and around the world, including new automotive technology, transportation legislation, emissions, fuel economy and auto repair.

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