Signs of a Bad Car Battery vs. Alternator

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John Davis
Updated on Oct 4, 2022 · 7 min read
Your car may have a bad battery if you experience issues like sluggish starting or dead interior lights and sound. On the other hand, you may have a lousy alternator if your engine dies while driving or the dashboard lights grow dim.
Battery and alternator problems with your car can be frustrating, especially if they cause you to be late for something important. These issues can be even more annoying if you aren't sure whether the cause is a bad alternator or a failing battery. Luckily, with the right know-how, it's relatively easy to spot the differences between these two issues.
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Bad battery vs. faulty alternator 

Your car's battery and alternator are essential components of its electrical system
While the battery provides the energy necessary to start the engine and power components like the security system, the alternator recharges the battery, supplies power to electrical accessories and components, and keeps the car running while driving. 
The failure of either one of these parts can spell trouble and even leave you stranded. The good news is that neither of these components is exceptionally difficult to repair, replace, or troubleshoot.

Signs of a bad car battery

Battery issues are definitely inconvenient and stressful. And with an average price range of $50 to $120, you probably don't anticipate replacing your car battery with much enthusiasm. 
You can save yourself some trouble—and money—by learning how to identify a faulty battery before taking your car to the repair shop or purchasing a new one. 
Here are the telltale signs of a bad car battery:

Battery age

The age of your car's battery has a lot to do with how well it functions. Over time, the battery loses its ability to retain a charge due to corrosion of its internals. Car batteries are designed to be replaced every 3-5 years. 
If you're experiencing difficulty starting your car engine, check the age of your battery. If it's more than five years old, chances are you need a new battery

It smells like rotten eggs

Another symptom of battery problems is a foul odor, specifically a smell like rotten eggs. While a rotten eggs smell from your car can be due to other issues, a leaking battery often causes it. 
The smell comes from sulfuric gasses that leak out of lead-acid batteries. A leaking battery can result from many things, including overcharging, physical damage, and cold weather.
If you notice a rotten egg smell coming from your battery or visible leaking, avoid contact with the battery and replace it as soon as possible

Hard to get the engine to turn over

If you have trouble getting your engine to turn over or your car starts slower than normal, you may have a bad battery. 
A healthy battery has enough power to start your car quickly and easily. If it takes an extended amount of time to turn the engine over, you likely need to replace the battery. 

Warped battery casing

A warped or swollen casing is an easily noticeable sign of a bad battery. This is usually the result of extremely cold weather or overcharging due to a faulty voltage regulator. 
If your car battery casing is swollen or distorted, you must replace it immediately. Do not attempt to drive the car in this condition, as the battery may explode and cause severe damage. 

Lights are dim

You may notice that your headlights or dashboard lights are dimmer than usual. This can occur if the battery voltage is too low to supply the necessary power to these components. 
If these lights don't turn on at all, you almost certainly have a dead car battery.

Noticeable battery corrosion

A classic cause of battery problems is corrosion. If you're having trouble starting your car, you should visually inspect your battery for this type of damage. 
Corrosion may look like white powder on the battery terminals or connections. You can attempt to
clean the terminals
and
jump-start your car
—however, battery corrosion is toxic, so be sure to exercise caution when cleaning corroded battery cables and terminals. 

You have to jump-start the car

If you have to jump-start your vehicle, chances are the battery is dead. And if the car runs—but only after a jump-start—it probably means your alternator is doing its job of keeping the engine running, but the battery can no longer hold a charge.

Signs of a bad alternator

If your car doesn't start, your first instinct might be to run to the car parts store for a replacement battery. But trouble starting your vehicle isn't always the result of a bad battery. A faulty alternator can cause similar issues.
Here are some of the most common warning signs of a bad alternator.

Stalled engine

Your car's battery is what supplies the power necessary to start the engine, but the alternator is what keeps your engine running once it's on. 
If you can start your car—either normally or with jumper cables—but it dies shortly after, you probably have a bad alternator.

Odd noises

A bad alternator can also cause strange noises. If you hear a squealing, growling, or clicking sound while trying to start your engine, you might have a failing alternator on your hands. 

Warning lights on the dashboard

If the battery light on your dash is turned on, it could signify a problem with the charging system. If your other interior lights appear to work normally, the issue could be a bad alternator. 

Electrical problems

Electrical problems—like issues with your air conditioner, power windows, or windshield wipers—can be caused by a faulty alternator. 
You might notice that these accessories work slowly or stop working entirely if your alternator isn't supplying the right amount of power. 

You have a dead battery (and it's new)

If your brand-new battery keeps dying, it's probably because the alternator isn't recharging it when the car is running
Modern vehicles require tremendous power to start—typically between 400 and 600 amps. If your alternator isn’t working, your battery has to work twice as hard to start the engine and keep the car running. This will quickly take its toll on a battery and cause it to die. 

Should you drive with a bad battery or alternator?

While you technically can drive with a bad battery or alternator, you should avoid doing so whenever possible. 
A bad battery can leave you stranded. And if you're somewhere without phone service or the resources to jump-start your car, you could remain stranded for quite some time.
On the other hand, a faulty alternator can cause a variety of issues with your vehicle's electrical components. In addition to stalling while you're in the middle of the road, a bad alternator could cause your headlights to fail at night—or even a power steering failure while navigating a sharp turn. Either one of these situations could be disastrous.
If you have any problems starting your car or keeping it running once it does start, it's best to resolve the issue as soon as possible. 
Key Takeaway Although it's possible to drive your car with a bad battery or alternator, doing so can result in electrical failures or leave you stranded on the side of the road.

How to find cheap car insurance

If your battery or alternator fails and leaves you stranded, a quality insurance plan with roadside assistance could really save the day. 
If you're overpaying for insurance coverage—or if your plan doesn't include this essential resource—it might be time to shop for a new policy.
But if the thought of insurance shopping sounds worse than being stranded on the side of the road, don't worry.
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When you download the Jerry app, just answer a few questions and we’ll get to work finding the best quotes for your coverage level across dozens of top providers. Select the policy you like best, and we’ll even do all the paperwork to get you signed up!
If you ever have questions or concerns, Jerry's licensed agents are always just a text away.
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FAQs

A bad car battery can cause your car to turn over slowly. It may appear corroded or even smell like rotten eggs.
If your car cranks slowly, has a battery that smells funky, or has dim headlights, the car battery may be about to die.

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