Car Battery Light On but Alternator is Charging – Causes + Fixes (+Photos)?

The red car battery warning light coming on yet the alternator is charging can be the start of anxiety and frustration for you the car owner.

Pinpointing the likely cause from the several possibilities in a timely and cost-efficient manner can be a challenge.

Some car owners have replaced batteries, alternators and found that the underlying problem was elsewhere.

So, in this post, I will go over:

  • the likely causes of the red battery light while the alternator appears to charge the battery (ordered to save you time)
  • checks and fixes you can do to fix the underlying problem, and
  • how you can protect your car’s charging system.

Car Battery Light On, Alternator charging – What else can happen?

Besides the car battery light coming on and the alternator charging, you may likely notice:

  • Low battery voltage ~12VDC overnight or when battery is left standing still
  • The car battery voltage may pick up when you drive the car for a while to as high as ~13VDC, a sign that the alternator is charging the battery
  • You can still drive on with several of the car’s accessories working – head lights, radio and possibly others another sign that the aternator is working

Why is My Car Battery Light On yet Alternator is Charging?

The red battery light coming on shows that there is a problem with the car’s charging system, affecting how well the battery charges.

There are a number of common reasons why this can happen:

  • loose battery terminal contacts with the alternator cables. This may be because they are corroded, just loose or failing within the insulation
  • loose wiring in 3-4 wire connector in the back of the alternator. There wires may be loose or broken
  • bad or failing battery
  • bad or failing alternator. Have your car’s alternator tested. Sometimes, they can appear to be working when they are not

The likely causes above are listed in order from easy and low-cost to the more involved and more expensive.

You can save some time and money when you work through the list above from the top to the bottom.

Is it Safe to Drive with the Car battery light ON (alternator charging)?

Much as you can drive your car, you should have it checked out as soon as possible because there is a likelihood that the underlying problem can get progressively worse.

How Long you can Drive with the Battery Light On?

In some cases, it may be possible to drive for days or weeks with the battery light still on if your car is not struggling to go into idle or showing signs of mistimings.

But depending on how severe the underlying problem is, you are risking the car’s engine failing to start or simply stopping in the middle of nowhere when you least expect it.

So, while you may be able to drive for several days or weeks, fix it right away especially if you make long trips or do a lot of night driving.

The headlights, heater add an extra load to the battery as you drive increasing the likelihood of failure.

What to Do when the Battery light stays On?

Can you Reset the Car Battery Light?

Some cars have a sequence of actions you need to take to reset the car battery light.

Always consult your car’s service manual.

However, many times, you only have to fix the underlying problem related to the car’s charging system – wiring, battery, alternator or otherwise.

When the battery light comes on and stays on, it is easy to go into panic mode.

But since your alternator is charging the battery, you should be able to continue driving without your car

Note: These are basic tests and are not meant to be conclusive – ALWAYS TO CONSULT A QUALIFIED CAR MECHANIC

No.ProblemCheckFix
 1Loose battery terminal contacts with the alternator cablesInspect the battery terminals, they should be clean without powdery coating on them  

Move the positive and negative cables connected to the battery terminals, they should be firm and NOT MOVE FREELY
Remove any powder on the terminals until they are clean.

Apply battery terminal grease

Tighten any loose battery cables
 2Loose wiring in 3-4 wire connector in the back of the alternator. They may be loose or brokenCheck the plug that fits into the side of the alternator is firmly plugged and not loose.    

Carefully pull the plug at the side of the alternator. Inspect the thin wires.  

You may have to tug at them gently to check that they are firm and they are not loose

(DO NOT ATTEMPT THIS IF YOU ARE COMFORTABLE WORKING WITH CARS)
Check that the plug is firmly fixed into the alternator side  

If there are loose or broken wires, replace with a new plug
 3bad or failing batteryCheck that there are no parasitic loads draining the battery

A fully charged car battery measures about 12.7 – 12.8VDC when measured with a good quality digital multimeter.  

Does the battery attain the voltage above?  

Is the battery able to hold the voltage of about 12.7VDC or does it drop to considerably lower?
(A sign of aging or failing battery).
      You can do a confirmatory test at the Autozone or by a qualified mechanic   Replace the battery with one recommended by the car manufacturer
 4bad or failing alternatorThe voltage across the battery terminals when the engine is running should be able 14.5VDC.  

If it is lower or considerably higher – this is likely a sign of a failing alternator that can damage your battery  

Measure the voltage of the battery (connected to the alternator) with the engine idle. It should read about 13.7VDC  

The battery voltage stays more or less constant, does not go as high as 14.5VDC

Note: These tests are not conclusive. You can have an alternator with the above output voltages that is bad or failing
You can do a confirmatory test at the Autozone or by a qualified mechanic    

Replace the battery with one recommended by the car manufacturer

How to Protect the Car’s Charging system?

While you have no control over factors such as ageing or failing battery or a bad alternator, there are steps you can take to prevent premature failure to your car’s charging system.

  • Avoid driving your car though high waters. These can damage your alternator
  • Avoid washing your car”s engine with high pressure water jets. They can also cause damage to the alternator

Also, pay attention to your car’s battery lifespan particularly if you have an older car. Batteries die after some time, so plan to replace them as recommended – don’t be caught off-guard.

Final Thoughts

If your car’s battery light comes and yet the alternator is working, there are a number of areas you can check to help you resolve the problem faster.

Check for loose or failing wiring on the battery terminals, alternator plug. Also, have the car’s battery and alternator checked.

Hope this helps!

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