How Does a Car Battery Work?

Our modern lives are jam-packed with electronic devices, nearly all of which most of us have no idea about their actual mechanism or function. We know what they do for us, and we know how to operate them, but when it comes to the nuts and bolts of their working, we draw a blank.

Among these many incomprehensible electronic items is one that sits at the heart of our car — the car battery. How does a car battery work? Outside of mechanics and electrical engineers, who knows for sure? In today’s article, we will explain in simple terms how these crucial components work.

First of all – What is a Car Battery

Your car’s battery is very different from the AA or AAA cells that you pop into the remote or your alarm clock. Its job is store chemical energy within its unit that it can then output to your car as needed to power the many electronic functions that your car and you depend on to get to your destination. In the past, it was mostly for the starter motor and then your lights, but now of course it powers all our modern conveniences, too — air conditioning, GPS navigation, touchscreen display, digital instrument cluster and more.

Broadly speaking, there are three types of car battery on the market today — lead acid, AGM and lithium-ion batteries. We will focus on what is still the most common, which is lead-acid batteries.

How does a Car Battery Work?

In a common car 12V battery, the most important element is the lead-acid chemical reaction that kick starts the power generation. These batteries are also known by their category name, “Starting, Lighting, and Ignition” or SLI for short. After giving an initial burst of power to get the engine moving, it outputs its energy in short bursts via its alternator. The main components for the SLI battery include six 2V cells (hence 12V in total), each with two plates/grids (one lead and one lead dioxide), and sulphuric acid which acts as a catalyst. The powering process happens across several stages:

Stage 1: A reaction starts when the plates become submerged in the sulphuric battery acid.

Stage 2: The lead dioxide plate creates ions and lead sulphate.

Stage 3: These ions subsequently react with the lead plate, making hydrogen and lead sulphate.

Stage 4: A further reaction takes place creating electrons, which then move quickly around the plates, forming an electric current.

Stage 5: The current flows out of the battery and to where it needs to be in your car.

As you likely know, if and when the battery runs out of juice, it can be recharged either with a trickle of low-amp power, or a more sudden “jump-start” method by using another car battery to assist. As long as the battery has a supply of power and a current being generated, it can be used continuously over four to six years.

New Technology

These days, asking “how does a car battery work?” is made even harder to answer by the emergence of new technology in the marketplace.

AGM Batteries: One alternative to the traditional lead-acid design is the cutting-edge Absorbent Glass Mat (AGM) lead-acid battery. This battery fundamentally uses the same principle as an SLI battery we described above, but with more advanced components that help the battery cope with the newest cars. Their invention was made necessary by the increasing complexity of cars thanks to the addition of ADAS systems, stop-start technology for heavy traffic driving.

The main problem that AGM batteries solve is the demand for batteries that can be stopped and started repeatedly without losing performance. The absorbent glass mat soaks up the battery acid to deliver constant contact between plats and electrolyte. Its generally more robust design makes it a better choice for the newest cars.

Lithium-Ion Batteries: Lithium batteries are at the heart and soul of electric vehicles, which while still in the minority of market share are set to become much more significant as the world continues to legislate on the future of car production. The UK, for instance, is planning to ban all internal combustion engine cars and hybrid cars by 2035, making EVs the only option. Until that time, they are only bound to get more prominent.

Their batteries work using the same physics and chemistry principles as other batteries do, but perhaps more innovative is their charging operation. Some Li-ion batteries reclaim kinetic energy when you hit the brakes. It’s usually not enough to reclaim a full charge but can keep the system working to extend its life on the road, especially in the city. Otherwise, these batteries are charged simply by plugging the car into the main electricity supply or via a charge point that you have installed at home.

How Does a Car Battery Work? They work Well, with Proper Care

Whatever battery type you have, proper car care will ensure they serve you well for years to come. Neglect of the lead-acid battery for example can mean corrosion and disrepair which affects power efficiency. That in turn directly impacts your car’s performance. Always have your batteries checked during a service, and look out for any signs of problems ahead.

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