Why Car Battery Light On But Alternator Is Charging? (Cause & Fix)

There’s a real correlation between battery & alternator when it comes to powering up the vehicle electrically. Like the CEL (Check Engine Light), the battery light also translates to one word – Panic! 

If you’re noticing your car battery light is on, but the alternator is charging & you’re looking for the possible causes with fixes, this article is for you. In this article, I’ll be explaining why this thing happens along with fixing methods.

Before diving deeper into this issue, let’s get started with the basics – the relation of battery, alternator & battery light in the following segment. Later on, I’ll cover the causes & fixes as well. 

What’s The Relation Between Battery, Alternator & Battery Light? [The Basics]

Two main electricity suppliers of your car are the battery & the alternator. The battery gives a push needed for engine start-up, whereas the alternator keeps the engine going. 

The alternator converts the engine’s mechanical energy to electricity & that electricity is stored in the battery. That being said, your engine won’t start if you have a bad battery & your car won’t continue running if you have a bad alternator. 

The battery light on the dashboard indicates a malfunctioning battery & battery charging system (faulty battery circuit). As you already know, there’s a correlation between battery & alternator; it’s okay to bind battery problems with the problems of an alternator. 

However, this assumption isn’t true most of the time. Sometimes battery light means you’ve only battery problems & the alternator is fine. The reason I said ‘sometimes’ is because you might have an alternator issue too & I’ll discuss everything in this article – Stay tuned!

Why Car Battery Light On But Alternator Is Charging? (Cause with Fix)

If you’re getting the battery light for a few seconds while turning on the ignition, it’s totally normal. You shouldn’t worry about it if the light disappears after a few seconds. 

If it stays on even after running for a few minutes, there’s some serious issue happening under the hood. Follow the next segment to know the possible causes of the battery light. 

Possible Causes Of Why Battery Light is On But Alternator is Charging

You already know there’s an absolute relation between the battery & the alternator. That’s why the battery problems can also mean alternator problems. 

Here are the possible causes (with short description & fix) of battery light is on but the alternator is charging:

Dirty or Corroded Battery Terminals 

Your battery terminals may be dirty or corroded. The battery is in a position where it can attract dust & dirt easily. Corroded battery terminals are one of the major causes of getting the battery light. 

Firstly, locate & remove the covers of the battery terminals & look for white or greenish substances. If you do find them, it’s them who are causing the battery light to appear. 

How To Fix:

Don’t touch them bare hand. Clean those corroded terminals with standard grease & your battery light problem should be fixed. 

Loosen Battery Clamps 

Sometimes this battery light can come even for a silly reason – yes, loosen battery clamps can turn the battery light on. Over time, the battery clamps get loose & it’s natural. 

How To Fix:

Tighten the battery clamps with the appropriate wrench. Don’t forget to use protective gloves before doing this task. 

Faulty Alternator & Alternator Parts

The alternator stores electricity in the battery. It helps keep both the battery & engine alive. That’s why suspecting the alternator for faulty battery & battery light is valid. 

Faulty alternator & alternator parts can cause the battery light to be activated. I’ll discuss it thoroughly in the following segment, just before the fixing part. 

How To Fix:

Inspect your alternator well & check if it’s really faulty. If it is, consider replacing it with a new one on your own or taking help from an auto shop. 

Damaged or Aged Drive Belt 

The serpentine belt (also known as the drive belt) helps connect the alternator & other important components to the crankshaft. Over time, this drive belt can age & cause the battery light to appear. 

How To Fix:

There’s no way of fixing a damaged drive belt or serpentine & you shouldn’t waste money on trying so. Simply replace the drive belt & you’re good to go. 

Faulty Battery & Battery Circuit

If you can’t start the engine at all, then it’s a problem with your battery & battery circuit. Possibly your battery is dead due to several reasons, including a faulty alternator. 

How To Fix:

There’s no way of fixing a dead battery. The Only thing you can do is replace the battery with a new one. Be careful while working with the battery & keep yourself safe from battery chemicals. 

How Can You Tell if It’s Caused By The Battery or Alternator?

As a follow up of the previous segment (the cause part), here’s the full discussion on – how to spot if the battery or alternator causes the battery light.

Let’s have a look at how to spot a dead battery step by step: 

  • Step 1: Take your technical service bulletin & check your car’s battery voltage. It should be around 13V. 
  • Step 2: Take your voltmeter or multimeter & measure the voltage of your car battery. 
  • Step 3: If you find 10.5V or lower voltage, you have a faulty/dead battery. More than 10.5 voltage indicates you still have a functioning battery. 

If you find out your battery is fine, it’s okay to suspect the alternator now. Here are the five symptoms of a bad alternator that might cause the battery light: 

  1. Dead Battery & Vehicle Won’t Start.  
  2. Growling, Squealing & Other Weird Noises From Under The Hood. 
  3. Sudden Warning Signs Such As “check engine,” “ALT,” & So On. 
  4. Failed Electrical Systems Such As Headlight, Air Conditioner, Power Windows & So On. 
  5. Stalling Engine Issue 

How Much Does it Cost To Fix Battery Light Turning On Situation? 

Depending on the causing factor/s of battery light turning on, the cost to fix depends. For your clearer understanding, here is the price chart of possible replacement parts: 

  • The Alternator Costs $150 to $350
  • Drive Belt or Serpentine Belt Costs $20 to $30
  • Battery Costs $150 To $250

Add an extra $200 to $500 of labor cost if you’re replacing the alternator by an expert. Besides that, replacing other parts will cost you $75 to $150 per hour if you’re getting them done from an auto shop. 

Can A Faulty Alternator Destroy A New Battery? 

Yes, a faulty alternator can destroy a new battery. It doesn’t really matter whether you’re getting a new battery or not – if the main electricity generator is faulty, your battery will become faulty too. 

As I mentioned previously, the alternator generates electricity & the battery stores them. Guess what will happen if the alternator is faulty & can’t produce the necessary amount of electricity needed?

Well, the battery will always function at a lower voltage capacity than recommended & it will badly harm the battery. Eventually, your new battery will be no more. 


In summary, battery light turns on to indicate malfunctioning battery & battery charging system caused by corroded battery terminals, loosen clamps, faulty alternator & damaged drive belt. 

I hope this article was helpful enough why your battery light is on, but the alternator is charging. Now you can fix those issues on your own or contact your nearby auto shop to do it for you.

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