Battery vs Alternator: Demystifying the Difference and their Functions

When looking at your vehicle's electrical systems, there are two crucial components that play distinct yet interconnected roles in starting and keeping your car going: the battery and the alternator.

Whilst both of these components are essential when it comes to powering your car, they both serve different functions, and many people don’t understand the difference between the battery and the alternator or even what they do in your car.

Having a clear understanding of the differences between the battery and alternator can help you diagnose possible electrical issues and give you reliable, enjoyable driving experiences well into the future.

So let's jump in and demystify the differences between these two components and shed a little light on their vital functions.

Your car battery is the electrical powerhouse for your vehicle

The battery is the heart of your vehicle's electrical system. It serves as storage for all of the electrical energy your car will need to start. It provides the initial power needed to start the engine and supports various electrical components when the engine is not running (your clock, odometer, etc).

The battery is primarily made up of chemical cells that help convert chemical energy into electrical energy through a chemical reaction (also known as a redox reaction). This stored energy is used to give power to the ignition process, lights, accessories and many other electrical systems when the engine is off, or it’s not generating enough power.

When you turn your key to start your car, the battery supplies a high amount of current to your starter motor, initiating the combustion process to get your engine going. When you first start your car, the battery acts as a power source for a short period, providing the necessary energy to turn the engine over. Once your engine is up and running, the alternator kicks in and takes over, making sure you have a continuous flow of electrical power to power the different components of your car.

Your alternator helps generate power on the go

Unlike your car battery which stores energy, the alternator is responsible for generating electrical power on the go whilst the engine is running. Unlike the car battery, which relies on chemical energy to create power, the alternator's primary function is to convert mechanical energy coming from the engine into electrical energy, helping to replenish the battery and power the electrical systems of your vehicle.

If we were to look inside an alternator, we would see it consists of a rotor, stator, and diode assembly. As your car engine runs, a drive belt connected to the engine's crankshaft helps drive the alternator's rotor, making it spin. This rotation creates a magnetic field, inducing an alternating current (AC or the Acca part in AccaDacca) in the stator windings. The AC power that’s generated in the stator is converted into direct current (DC) by the diode assembly, which is then used to charge the battery as you’re driving, ensuring it remains at optimal levels.

Note: This is why a ‘flat’ battery can sometimes be jump-started and recharged by driving your vehicle around, as the alternator helps create energy to recharge your battery.

As you’re driving your car around, the alternator also supplies power to your electrical systems, including lights, the audio system, air conditioning and many other accessories. The alternator also powers the ignition system and helps to recharge the battery after the engine has started, making sure your car is ready for the next ignition cycle.

The symbiotic relationship between battery and alternator

Many people don’t realise that under your bonnet, the battery and alternator work in harmony to maintain all the electrical needs of your vehicle. Whilst the battery is responsible for initiating the engine start-up and helps provide power when the engine is off, the alternator takes over once the engine is up and running, keeping your battery charged and producing the electricity needed to power the various electrical systems found in your car.

It's worth noting that often, a faulty alternator puts unnecessary strain on your battery, leading to a weakened or discharged battery over time, which can leave you stranded in a carpark somewhere.

Similarly, a weak or malfunctioning battery can often cause the alternator to work harder, often leading to alternator failure.

What can you do to make sure your car’s battery and alternator runs smoothly?

Conducting regular maintenance and inspections of both your battery and the alternator can help to pick up any minor issues before they become major problems and keep your car running at optimal performance.

Diagnosing issues to ensure reliability
Now that you have an understanding of the difference between the battery and alternator, this can help you diagnose potential electrical problems in your vehicle. If your car has trouble turning over or you notice dimming lights inside or out, this could be an indication of a weak or dying battery.

Likewise, if you observe battery warning lights on the dash, flickering lights or electrical malfunctions when the engine is running, this typically points to alternator issues.

If you run into any of these issues, it's always wise to consult a qualified mechanic who can perform the appropriate diagnostic tests to determine the root cause of the problem. If it turns out to be a battery issue, Allstar Batteries is sure to stock the best battery for your vehicle's make and model.

We have the northside of Brisbane covered when it comes to your battery requirements so drop into one of our main stores at Brendale, Caboolture or North Lakes.


12 Garret Street
Brendale Qld 4500
Ph: 0413 692 236


6/106 Lear Jet Drive
Caboolture Qld 4510
Ph: (07) 5309 4905


12/88 Flinders Pde
North Lakes Qld 4509
Ph: (07) 3048 2293


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