Is It a Car Alternator or Battery Problem - How to Tell

Your car alternator and battery are part of the vehicle’s electrical system. Unfortunately, they share similar symptoms when either one of them fails. So, how do you tell if it's a car alternator or battery problem?

There are unique symptoms to look for when a car alternator or battery fails. It’s a bad alternator if your car stalls after starting, headlights flicker or dim, or you notice electrical malfunctions. A bad battery triggers the warning light to turn on or the in-car entertainment system to reset.

Spotting the different symptoms can save you a lot of trouble. So first, this guide will help you understand the unique purposes of the alternator and battery. Then, you’ll learn how to differentiate between alternator and battery failure symptoms.

Let’s get started.

Battery Vs Alternator: What’s the Difference?

Before we dive into the symptoms of a problematic car alternator or battery, let’s refresh our understanding of the purposes of those two parts.

An automotive battery is designed to send the massive electrical charge that starts your car. That charge flows to the car’s starter, which turns the engine and gets it started.

Because the car battery sends that strong jolt of power to get things running, it’s also known as a ‘starter battery’.

However, once your car is running, the alternator becomes the star of the show. 

The alternator supplies electricity back to the battery for it to recharge, enabling it to supply the car’s electric parts like headlights, wipers, and more.

How Long Do Alternators Usually Last?

Alternators typically last about 7 years or between 150,000 and 250,000 kilometres. Naturally, that lifespan depends on how much wear and tear the alternator experiences.

Those that are overused or used incorrectly will start to give you problems sooner.

How Long Does a Car Battery Usually Last?

Car batteries usually last between 3 and 5 years. As it reaches the end of its lifespan, a car battery gradually loses its ability to hold an electrical charge.

Despite the 3-5-year lifespan, a car battery can also become faulty much earlier if you don't use it (e.g., in a rarely driven car) or use it too much.

How to Tell If It's Your Alternator or Battery

At this point, it should be clear that your car battery and alternator are two separate components, each with a unique purpose.

Despite that, it can be pretty confusing to know which one is to blame when there’s a problem. That’s because the alternator and battery are both parts of your car’s electrical system. So, when there’s a problem, many bad alternator symptoms overlap with weak car battery symptoms.

For instance, bad batteries and alternators lead to electrical issues throughout your car, especially when starting the engine. As a result, pinpointing the root cause can be challenging at times.

Thankfully, some of those symptoms are unique to either the battery or the alternator. So when you know which ones to look for, you can then find the root of the problem.

Signs of a Bad Battery (And Not a Bad Alternator)

Here are a few unique faulty or weak car battery symptoms that make it clear that the problem isn’t with the alternator:

1. Battery warning indicator: Most car models come with battery warning indicators, typically on the instrument panel. So, when your car has electrical problems, and the battery warning light or indicator is active, the root cause is likely the battery.
2. Old battery: The age of your battery is another clear hint. Car batteries last 3-5 years, and they'll wear out sooner if you rarely use them. When you know you've got an old (or seldom used) battery onboard, the electrical problems aren't coincidental.
3. Sulphur smell (rotten eggs): Faulty car batteries will give off a sulphur smell, which most people recognise as the smell of rotten eggs. Alternators don’t give off such smells, so there’s no doubt that you’ve got a battery problem on your hands.
4. Windows are slow to move: Your car’s electrical parts, like its window motors, receive power from the battery. A faulty battery can’t deliver that power effectively, so parts like your car windows will move slower than usual.
5. In-car entertainment system resets itself: Lastly, check your in-car entertainment system. The system can only save your settings and presets when it receives uninterrupted power from your car battery. So, if you notice it reset itself, that indicates a battery problem and not one with the alternator.

Signs of a Bad Alternator (And Not a Bad Battery)

Here are some telltale signs that the problem is coming from your alternator and not the battery:

1. The car starts briefly but stalls: A bad battery or alternator can cause problems when starting your engine. But if the engine does start briefly before stalling out, that’s a clear sign your alternator is to blame.
2. Dim lights: Your headlights are another excellent place to check for symptoms of alternator failure. They’re connected to the alternator and will flicker or dim if there’s a problem there.
3. Electrical issues: Other miscellaneous electrical issues around your vehicle can also point to a problem with the alternator. For example, some auto accessories will malfunction when they don’t receive the correct amount of electricity. If that happens, it’s likely because the car alternator isn’t sending enough power to the device.

When you learn to distinguish between a bad car alternator or battery, you’ll get to the root of the problem quicker. But, more importantly, it’ll also prevent you from spending money unnecessarily by purchasing the wrong spare parts.

Whether you’re looking for a new car alternator or battery, you can start looking for the part at CarPart AU. For example, you can go to our Marketplace and find used or new alternators, such as this one for an Audi Q5. Or you may also send a request through the Part Finder for any car part you need.

By Ray Hasbollah