Car Battery 101: How Do Car Batteries Work?

You probably don’t think much about your car battery, but it’s the only thing that gets the power going for your car to start. If you’ve ever had a problem with your battery, you probably already know that without your battery, your car really can’t do anything.

If you’re going to look after your battery, you need to know how they operate, when you should replace yours and what your options are.

What is a Battery?

A battery is a device made from chemical reactions that create electrical energy. The way that a battery produces electricity is by using an oxidizing-reducing (redox) reaction, in which electrons move between two different materials through an electrical circuit.

A lot of the time, people use the word battery when they actually mean a cell, which is the part of a battery that stores and releases electric energy.

When trying to figure out how cells and batteries differ, think of a battery as a collection of one or more cells that have been connected together to achieve a certain voltage or capacity.

What is a Car Battery?

A rechargeable battery used in automotive applications to power the starter motor of an internal combustion engine (ICE) is known as a car battery. The primary function of the car battery is to supply electrical power to the starter motor, so it can engage with the ICE and begin moving the vehicle.

The alternator supplies power to the car’s various electrical systems once the ICE is running and the alternator will recharge the car battery depending on whether the electrical load is increasing or decreasing.

The majority of car batteries use lead-acid batteries; within each lead-acid cell there are two terminals. Each terminal consists of plates composed of lead and lead dioxide, both of which are submerged in a sulphuric acid solution that serves as a catalyst for the lead-acid cell.

When the lead and lead dioxide plates are combined, they generate electrons which produce electricity and then flow from the battery to the starter motor to generate torque to spin the ICE. As the chemical reaction is reversible, the lead-acid battery recharges itself after being used to crank an ICE, and can be jump-started when it has a flat charge.

When you turn on the ignition, it sends a signal from the battery to initiate the chemical reaction. The resulting electricity is directed to the starter motor, which then turns the engine and directs voltage to the ignition coil. The ignition coil creates enough voltage to send an electrical charge to the spark plugs, igniting the mixture of air and fuel in the ICE combustion chambers.

How Do Car Batteries Work?

The majority of automotive batteries use lead-acid chemistry to operate. They are classified as “SLI” batteries, where “SLI” stands for “Starting, Lighting, and Ignition.” SLI Batteries are used to provide short, high-energy bursts to start the engine, power lights, and accessories.

An SLI Battery is designed for a single use — to provide the jolt needed to turn the engine over and get it started; from then on, the alternator supplies power to the vehicle. Most new vehicles come equipped with a generic SLI battery when they leave the factory.

How do Car Batteries work?

Six individual cells make up a normal vehicle battery. Normal vehicle batteries produce energy from six cells, producing 2 volts of energy per cell, giving the user 12 volts of electricity.
The lead plates, submerged in acid, will create an exothermic reaction with the lead acid, causing the two metals to combine with one another as well as with the production of lead sulfate.
Lead ions produced are attracted to the opposite lead plates and will “combine” partially forming hydrogen gas and lead sulfate.
The overall process creates an exothermic reaction which produces electrically-distributed electrons that flow through the circuit upon cranking of your engine or powering on the headlights or radio.
Because all chemical reactions that occur, leading to the production of power, from original discharge and during the reclamation process, to all subsequent discharges of batteries are completely reversible, batteries can be recharged over and over again throughout their lifetime by applying direct current to the battery with the correct voltage parameters (both lead to combinations of lead and lead dioxide on plates).

Are There Any Warning Signs That May Indicate My Battery Is On The Fritz?

There is no substitute for experience. We’ve all had one of those moments where, “If only I had known this sooner”. Fortunately, there are many signs or symptoms available to you that may be a precursor to your battery’s demise:

Slow Engine Crank – When trying to start your vehicle, you will notice that the engine cranks slowly and it takes longer than normal to start the engine. You would probably describe the sound as the “rur rur rur” kind of sound.
Check Engine Light – With weak battery power, you may start seeing check engine lights pop up here and there. Check engine lights and other strange system indicator lights (low coolant lights) can indicate that the problem is in your battery. However, other issues (such as needing coolant) can also trigger these lights.
Low Battery Fluid Levels – Car batteries usually have an opaque portion in the casing, making it easy to monitor the fluid levels in your battery. If the translucent section is cloudy or opaque, you know that the battery fluid levels need checking. (If the caps are sealed, there is no way to check whether the battery fluid levels are low.)
Fluid Levels below the Lead Plates (Energy Conductor) – If the fluid levels of your car battery have dropped below the lead plates (the part of the battery that gives it energy), this indicates that the charging system needs testing. Unless you check the fluid levels, it’s hard to say why the fluid levels have dropped.
Swollen Battery Casing – A swollen battery casing can also indicate that a battery has gone bad. A swollen battery casing is generally caused by heat from intense charging, which reduces the length of time (reduced battery life) that your battery will function properly. You will be able to determine whether the battery casing is deformed when looked at from the side.
Odors – If you notice a strong odor around the battery that resembles that of a rotten egg smell (sulfur), this could be a sign of battery leakage. Leaking batteries will also corrode around the terminals of the battery, resulting in a possible need to clean the terminals or you may have to replace your battery.
Old Batteries – If your battery has been in use for over three years, it is likely an older battery. Although batteries can last upwards of three years, it is important to check the current condition of a battery at least once a year for any signs of wear and tear when it reaches three years old. The length of time for which a battery lasts will depend on a variety of factors, including the types of driving, driving behaviors, the weather, and short trips (less than 20 minutes) that will significantly shorten your battery’s normal lifespan.

Why do batteries go flat?

While car batteries typically have a service life of five years or longer, the length of time a battery lasts also depends on a few other factors such as its maintenance and care. In addition, depending on the type of trips you take, it’s possible to see your car battery age at as early as three years.

When you use your vehicle battery to start the engine, the entire energy stored in the battery is depleted, so if you frequently take short trips, your vehicle will not have an opportunity to fully recharge the battery before it is used again, which means that your battery will be depleted at a faster pace than if you took longer road trips.

Temperature and how much extra electrical load your vehicle has also affect the way car batteries operate.

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How Do I Determine If My Battery Is Too Old?

You may wish to refer to the four-digit or five-digit date code written on the outside of your battery case. The first half of this code refers to the date your battery was shipped to our local warehouse and consists of a letter followed by a digit.

The letter represents the month (A = January, B = February, etc.). The second part is the year (9 = 2009, 1 = 2011) that the battery was shipped. There are also 1-3 digits at the end of the code to indicate where the battery was manufactured.

Most car batteries will last three to five years. Here are ways to identify if your battery is weak: It takes longer than usual to crank your engine, there is low fluid in the battery case, the battery case shows signs of bulging, you smell sulfur (rotten eggs), or you see the check engine light on your dashboard. Batteries over three years old should be monitored closely.