Can A Bad Alternator Drain Battery? (2 Easy Ways to Check)

A car’s ignition system largely depends on the function of the battery and the alternator. While the battery starts the car and provides power to the electrical systems, the alternator charges the battery when the engine is running by converting mechanical energy into electrical supply.

However, if you have a bad alternator, you may find the consequences costly. The batteries won’t be charging while running which results in the stopping of the vehicle suddenly as the battery finally gives up.

That’s not the only problem you’re going to encounter. A bad alternator can drain the battery even when the car isn’t running.

However, can a bad alternator drain a battery? How to test an alternator? How long does it take for a bad alternator to drain a battery? If you’re searching for the answers to these questions, this article is a must-read for you.

Can A Bad Alternator Drain Battery

how to check if alternator is draining battery

If you’re facing trouble with your car’s performance, you should be worried about the batteries and alternators. But how to tell if the alternator is bad and how to check if the alternator is draining the battery?

There’re two easy methods to check if the key component is bad and it’s draining the batteries.  

The first test can be done at your garage. You need to start the car by keeping the hood open. Then, while the engine is running take away the negative battery terminal cable from the 12V battery. If the engine operation stops, the alternator is likely to be bad. It’s draining the batteries as they can’t supply enough electricity to keep the engine running on its own.  

The second one is the most popular method for testing alternators whether it is in good condition or dying. However, you need to remove it from the car to get it tested. Once you connect the alternator to a terminal, it should show between 12 to 13.5 voltage scale. Any number less than that indicates it’s not capable to charge the level of battery completely. On the other hand, any number more than that indicates it’s overcharging the 12V battery. In both cases, it drains the long-term battery life.

Signs of A Bad Alternator

Well, now you know that a dead alternator is a threat to the car batteries, electrical device, electrical current, and overall performance. But, how do I know if my alternator is draining my battery? There’re some bad alternator symptoms to let you know that it’s going bad.

If your car’s alternator is bad, you should experience the following signs:

  • If the car starts easily but the warning sign on the dashboard comes on straightway, the problem lies with your alternators, not the bad batteries.
  • If you’re driving at night and see the bright headlights are dim, suspect the alternator, not a faulty battery.
  • Modern vehicles automatically shut down important features like air-conditioning, ABS with strange noises just to ensure most power gets utilized to run the engine operation. If you find this phenomenon in your vehicle, consider the alternator is going bad.
  • While running the car, if you find the brightness of the dashboard lights gradually dims, it’s likely to be because of the faulty alternator.
  • You might get the smell of burning rubber if it is overheating.
  • Before happening the incidents, you’ll hear unusual noises.

What Causes an Alternator to Go Bad?

There’re a few reasons behind that accelerate the alternators to go bad. If you know the causes before it’s too late, you may save it from going dead. Here’re the major causes:

  • Many times, you get an alternator belt that is too tight. It may hold the part securely but may ruin the bearings of the electromagnetic system.
  • There’ll be dirt, dust, and oil on the parts with time. These unwanted particles prevent the alternating machine to operate at an optimum level. If you’re living in a polluted area, you may face the problem frequently.

To get rid of the causes that may ruin the machine, you should regularly have service your vehicle. Check the drive belt tensioner so that it doesn’t stay tight too much. Also, try to clean the vehicle whenever you get time to keep the dust away.

How To Fix An Alternator That Is Draining The Battery

You can fix an alternator yourself or ask for help from a repair shop. The process is simple and straightforward if you have a serpentine belt diagram to reinstall correctly. Replacing an alternator cost may be pricy if you visit a repair shop.

The faulty alternating device needs to be disconnected from the dead car battery and removed from the serpentine belt. Then, unbolt the device carefully and eliminate the wired connectors. Finally, you only need to re-install everything in reverse. You can expect to get rid of the faulty diode.

Note:  You need specific diagnostic and repair information for your car while doing this. ALLDATADIY is a great site with complete manuals of over 30,000 vehicles from which you can easily get yours.

Watch the video of alternator replacement for a better understanding.

Tips for Longer Driving with A Bad Alternator

How long will a battery last with a bad alternator?

The answer varies depending on the type of the engine, how old it is, and how many electronic systems are in the car. If you have a classic diesel engine, you can expect to run for several hours with a bad diode because of the simple engine operation structure. Again, modern patrol cars and hybrid vehicles may last as little as half an hour as it has spark plugs to drain the weak battery faster.

Here’re some tips for you to run longer with a bad alternating machine.

  • When you start the engines, try to use a jump-start booster.
  • While driving use features like headlights, fan, radio that run with electricity as little as possible.
  • When you drive faster, you cover more distance within a given time. However, maintain the speed limit always.
  • Change the bulbs with LEDs that consume less electricity.

Frequently Asked Questions (FAQs):

What Is Key-Off Battery Drain?

What can drain a car battery when the car is off? There’re many things such as radio presets, security alarms, clocks continue to draw power from car batteries even after the car is turned off. This cumulative load that drains the battery is called a Key-Off battery drain or parasitic drain.

What Is an Alternator Exciter?

Exciters are small generators that are mounted on the same shaft as that of the alternators to provide a stationary rotating magnetic field.

What happens to the radio and other electronics if I have to disconnect the battery?

When you disconnect the batteries, radio, clock, dim headlights, and other electrical components lose power. So, you need to reset the clock, enter the radio code for the audio system when you connect batteries again.

Will bad alternator diode cause parasitic drain and still charge battery?

Faulty diodes or alternators cause a parasitic battery drain. However, it still charges the battery when the engine is running until it’s completely dead with strange noises.

Can a bad alternator drain a battery when the car is off?

While a diode allows current in one direction, a bad one keeps charging the electrical circuit even when the engine operation isn’t running. A bad alternator diode draws charges from the battery even when the car is off. You may find the car isn’t starting in the morning.

Final Words

So, can a bad alternator drain a battery?

Yes, it does and is one of the main reasons to cause the battery going dead. Make sure to have the alternator test of the engines if you see any symptoms discussed above before it’s too late for a dead battery. Thank you.

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