How Car Batteries Work

What’s In a Battery?

All batteries are composed of three basic components. Whether you’re looking at the tiny batteries in your key fob or the sizable one in your car, you can expect to find these three elements:

• Anode
• Cathode
• Electrolyte

When electricity is discharged from a battery, electrons are released from the anode and travel to the negative terminal. Ions are also released into the electrolyte. This process is called an oxidation reaction.

On the positive terminal, the cathode is responsible for accepting electrons. This flow of electrons completes the circuit. The electrolyte is an essential part of the battery that bridges the gap between the anode and cathode. It creates equilibrium between the two terminals and prevents electrons from jumping directly from the anode to the cathode, meaning current must travel through a circuit to reach the terminal for the cathode.

Many batteries you purchase are disposable. These batteries work in a single direction and have a limited amount of reactants. Once they run out of these reactants, they can no longer use chemical energy to produce electrical energy.

Electrical energy comes from the movement of electrons from one object to another. A good conductor creates a more efficient flow, but electrons can flow through a great number of materials. The copper or other ductile metal in your wiring makes a great conductor, while the rubber coating doesn’t. Our bodies are excellent conductors, so it’s essential to always wear protective clothing and be cautious around batteries and electrical wiring. Touching the two terminals of your battery together with a conductor can create an electric circuit and poses a risk of electrocution.

Basic Parts of a Car Battery

Your car battery, like most batteries used in modern electronics, is a rechargeable battery. This allows them to become recharged and continue to work far longer than a disposable battery. Here are the basic steps to understanding how a car battery works.

A car battery is attached to your vehicle’s SLI electrical system, or starting, lighting and ignition system. Your vehicle uses an alternator to supply power to the battery and your SLI system after ignition. A typical car battery is called a 12-volt lead-acid battery.

While new car battery types are being used, most standard SLI batteries have six cells inside their case. These cells are all made of a lead plate and a lead dioxide plate. These plates, also called grids, work together to create two volts for each cell. That’s why a six-cell battery is also called a 12-volt battery.

The lead plates of your lead-acid battery are submerged in sulphuric acid. This acid acts as a catalyst and triggers the reaction between your lead and lead dioxide plates. The result of this reaction is ions and lead sulphate.

The ions in this reaction form a chemical reaction with the plates and create hydrogen. This chemical reaction produces electrons. It’s these electrons that bridge the gap between chemical reaction and electrical reaction. They speed around the two plates and create electricity, which is sent through the battery terminals and into your entire SLI system.

Unlike a disposable battery, this reaction is reversible. With proper use, your car battery can last three years or more, as long as there’s no physical damage to the exterior of your battery.

What Car Batteries Do

The battery has two main functions:

• Supply power to the starter so that it can start the vehicle
• Store electrical energy for running accessories in case of electrical system failure and/or when vehicle is not running

Different battery designs, which include type, size, and power requirements, exist for every vehicle. For the battery to do an effective job powering your vehicle, the correct battery must be used. You can find the right one by using AutoZone’s battery vehicle fitment lookup while browsing our selection.

Battery Design Considerations

Group Size: Size refers to the dimensions of the battery. It indicates length, width, height, and post configuration (which side the +/POS and -/NEG terminals are on). This ensures consistency among manufacturers the same way AA, AAA, etc. batteries are used for the batteries in your remote controls, flashlights, and so on.

Cold Cranking Amps (CCA): Cold cranking amps is the amount of power (amperage) that the battery can deliver consistently over 30 seconds in cold (0F) temperature. The higher the CCA, the better a battery will be able to perform in extreme weather conditions.

Reserve Capacity (RC): Reserve capacity is the amount of time that the battery can supply power to the vehicle when the key is off, or if the charging system fails. The technical definition is “the number of minutes a battery at 80 degrees can be discharged at 25 amps and maintain a voltage of 10.5 volts for a 12-volt battery”. The higher the reserve capacity, the longer the battery will provide power before needing a charge and the longer the vehicle will operate on the battery power alone. This is an important factor to consider for a vehicle with accessories that require extra electricity such as light bars, winches, etc.

Note: Having the correct group size battery with more CCA and reserve capacity provides assurance to overcome potential electrical system problems. The higher CCA and RC you have, the better off you are when you encounter extreme conditions that might cause lower power batteries to fail.

How the Weather Affects Batteries

Heat is the number one cause of battery failure, and extreme heat can cause the water in a battery to evaporate. This can lead to corrosion of the internal components and battery failure.

Cold temperatures dramatically reduce the effectiveness of a battery. Electrons flow slower, reducing the amount of energy a battery provides. This results in a reduction of cranking power and sluggish starting. Batteries left in a discharged state are also susceptible to freezing, which damages internal components.

Dangers of an Old Battery

Although the chemical reaction can be reversed for a long time, you should still be cautious using an older car battery. Most warranties last up to three years, after which it’s a good idea to find a replacement. Your battery may still be working effectively, but it’s subjected to harsh temperature changes, bumps, and jolts while in your vehicle. Over time, your battery may crack, causing the acid to leak out into your engine compartment.

Because your car battery uses both lead and sulphuric acid, it can be hazardous to remove a damaged battery without proper protection. You’ll also need to find a safe way to remove, store, and dispose of your battery. Don’t place a battery on its side or top. When handling a battery, it’s always a good idea to wear protective clothing, just in case. This is particularly true of older batteries, which may not be sealed. Old car batteries have a loose lid that can be easily opened, which could easily cause you to come in contact with lead and sulphuric acid.

To dispose of your old battery, bring it to your local AutoZone and consider swapping it for a new one. Don’t wait until your battery ceases to function, look for warning signs that it may be time to upgrade your 12-volt car battery.

Other signs of a battery that needs to be replaced include corrosion around the terminal or a short battery life. If you find your battery quickly runs out of power when your engine isn’t running, it may be time for a new battery.

Find a New Battery Today

Now that you know the basics of how batteries operate, you understand a little more about your remarkable vehicle. Your car battery is an essential part of your ignition system, so without it you won’t be able to start your vehicle reliably. A dead car battery can leave you stranded, so it’s an important part to keep up-to-date and well maintained.

If you’re not sure how old your battery is, or whether it’s still operating efficiently, stop by your local auto parts store. At AutoZone, we’re happy to not only test your battery, but also help you remove your old battery, find the right car battery, install your new battery, and safely dispose of the old battery. Don’t wrestle with an outdated battery on your own, take it to our professional team and enjoy long-lasting, hassle-free electricity for your SLI system. You can get the parts you need at your local AutoZone Store. If the job is too big for you, seek out one of our Preferred Shops to help you do the job.