Why Does Car Battery Keep Dying But Alternator Is Good?

So, you’re sure that the alternator of your vehicle is working perfectly but you’ve been noticing that the battery keeps dying. Frustrating, we get it. But what’s the mystery? Why does car battery keep dying but alternator is good?

Your car may have a loose or corroded battery connection, or the battery is faulty may be. Other reasons for this issue are drained batteries, parasitic drains, extreme weather, or you’re not giving enough time to recharge the battery.

So, let’s get deep into the topic and talk about it in detail. This article will cover the common reasons for the issue, how you can identify the issues, and how you can get rid of them.

Let’s dive right in, mate!

Why Does Car Battery Keep Dying But Alternator Is Good?

Before we just head into the details, here’s an ‘at a glance’ option for you to see what’s wrong with your car battery and what to do.

ProblemHow to identifySolution
Faulty batteryUse a multimeter to check the battery.Replace the faulty battery with a new one.
Loose or corroded battery connectionsCheck for green, blue, or white blooms around the corroded materials.Clean or tighten the terminals of the battery.
Parasitic drainUse a test light or a multimeter to check the current flow.Isolate the circuits that are draining power.
Drained batteryDetermine the age of the battery, and check if it produces a smell like rotten eggs.Jumpstart your vehicle or get the electrolyte level fixed.
Extreme weather conditionsCheck if the components are malfunctioning or if the engine oil got thickened for extremely lower temperatures.Change the battery if it’s too old or get it checked by a mechanic if you’ve recently got the battery.

6 Reasons Why Your Car Battery Keeps Dying When Alternator Is Good

If a relatively new car battery dies suddenly, the first thing anyone will check is the alternator. However, upon discovering that the alternator is good and running well, the question will arise as to why the battery is dead. There could be a few reasons behind the car battery dying. 

6 Reasons Why Your Car Battery Keeps Dying When Alternator Is Good

If a relatively new car battery dies suddenly, the first thing anyone will check is the alternator. However, upon discovering that the alternator is good and running well, the question will arise as to why the battery is dead. There could be a few reasons behind the car battery dying. 

1. Bad or Faulty Battery

The car battery provides the current necessary to operate the car. It is constantly being discharged and partially charged. Over time, the insides of the battery get corroded and weak. 

If the battery is old and damaged like this, no matter how much current the alternator provides to it, the battery won’t hold the charge. In such cases, even small and minor drains (such as the memory function in the radio of your car) can damage a weak battery.

Worth noting, a faulty or weak battery can cause explosions. So, make sure you’re equipped with protective gear while dealing with the inspection or troubleshooting on your own.

How to Identify

You can test your car battery at home or get help from an auto service shop. For the DIY project, you need to use a multimeter. Now, follow the steps below:

  • Set your multimeter to 15-20 volts.
  • Then, find the positive and negative terminals of the battery and insert the multimeter into the terminals. And, read the voltage now.
  • You need to have an idea about what should be the voltage of your battery. You can get a recommendation from the owner’s manual; it’s 12.6 volts in most cases.

If the volts indicate a faulty battery, it might need a replacement.

How to Resolve The Issue

Replacing a faulty car battery with the right battery can be the solution. Make sure the size of your new battery matches the size guidance of the owner’s manual. Also, the battery should have the right number of cranking amps for working properly.

Now, here’s how you can replace a faulty car battery on your own:

  • Park your vehicle first and turn the engine off.
  • Use battery pliers or a wrench to detach the negative cable of the battery. You can simply do it by loosening the nut. If you notice corrosion or dirt in the parts while doing it, clean them away using a solution of water and baking soda.
  • Now, disconnect the positive terminal of the battery in the same way.
  • Unscrew the battery clamp using a wrench or socket.
  • Now, you’ve got the right space to remove the dead battery. Gently, lift the faulty battery from your car and remove it. Then, clean up any residue or corrosion from the place.
  • Install the new battery and make sure you tighten all the hardware so there’s no movement.

2. Loose or Corroded Battery Connections

The battery cables or connections are the media that help in the transfer of electricity from the battery to your vehicle. When the terminals (positive and negative) of the cables are loose or there is built-up corrosion, your car will not get enough power from the battery.

The most common reason for such loose connections can be bumps, vibrations, and rattling of the battery that is the result of an uneven roadway.

And, the reason for the corroded connections is either a release of hydrogen from the sulfuric acid in your battery’s fluid or overcharging.

How to Identify

Checking for loose or corroded car battery connections can be a bit tricky because the corrosion may or may not be noticeable in some cases. On the contrary, you can notice green, blue, or white blooms of corroded materials sometimes.

The corrosion can be noticed around the connectors, cables, or battery terminals. If you notice any corrosion between the cable connectors and the battery terminals, it will weaken the starter motor’s ability to flow current from the battery. It also can interfere with eh ability of the charging system as well.

How to Resolve The Issue

What you can do about the loose or corroded connection is you can clean or tighten the terminals of the battery. And, here’s how.

  • First thing first, check how tight both the terminals of your vehicle are.
  • Make a solution of water and baking soda. Take 1 tablespoon of baking soda and add 1 cup of water to it. Then, mix the water and soda thoroughly to make a blend of them.
  • This time, you need to gently scrub all the corrosion off the terminal using a battery brush, any kind of stiff-bristled toothbrush, or a wire brush.
  • Once cleaned, locate the cable that needs to tighten. It usually is on the side where the battery terminal is separated or cut. It can also be on the opposite side of the cable anchor point sometimes.
  • Now, use the correct size wrench to tighten the bolt and keep tightening it until you can’t move the terminal with your hand.

3. Parasitic Drain

A parasitic drain occurs when the engine has been turned off but the car still drains charge from the batteries. When the engine is turned off, the alternator doesn’t recharge the batteries anymore. So, if there is something in the car that drains more charge from the battery, it reduces the lifetime of the battery. 

Parasitic drains can happen because of a short circuit, a running interior light like the glove box, or the trunk light. Sometimes you might accidentally leave the headlights on or forget to turn off the radio. 

Things like this cause the battery to drain overnight so the next time, you might find yourself unable to start the car because the battery is dead.

How to Identify

If you ask about the simplest way of checking for a parasitic drain, just detach a battery cable and start checking for current flow. You can use a test light or a multimeter for this job.

However, the result from a test light might not be precise.

Make sure you use the highest amperage setting if you use a multimeter to check the current flow. Otherwise, there will be a risk of blowing a fuse (that’s expensive, of course) inside the meter.

How to Resolve The Issue

As you already know how parasitic drainers work, you’ve guessed the solution probably. Yes, you need to isolate the circuits that are draining power.

Take the advantage of a multimeter here. Pull one of the fuses each time and inspect what the multimeter does. The amperage will drop drastically if there’s a parasitic draw. 

However, if this is not the case for you and you don’t see any amperage drops, see if the amperage is under 100mA. If it’s not under the 100mA threshold, sorry but there are several parasitic draws you need to deal with.

Isolate the specific circuit that’s causing your batteries to drain. You can prevent parasitic drains easily though.

Unplug the chargers, cell phones, and other optional equipment when you park the vehicle overnight. Also, don’t forget to fully close the glove box, trunk, and doors of your vehicle. Turn off every light of course!

4. Drained Battery

If you leave a car battery unused for too long, it will start to deteriorate after about a month. Even if the car is not running, the battery always draws a small amount of current in itself. 

When you don’t drive your car for a long time, the current eventually drains the complete battery and leaves it dead. Since the ignition isn’t turned on, a good alternator can’t recharge the battery here either.

Moreover, the battery will drain too fast if you store it somewhere in excessively hot or cold temperatures. Excessive parasitic drain on your battery will also cause it to be dead.

How to Identify

Well, there are some common signs that show up if you have a drained or dead battery. Below are some of them.

  • If the battery is too old to work properly, you need to replace it because it’s almost dead. The average lifespan of most car batteries is 4-6 years, it varies though.
  • Dead batteries produce smells like rotten eggs. There are sulphuric acid and water in all lead-acid batteries. When your battery is in charge, it produces H2S and the gas is responsible for the rotten egg smell.
  • Check for blue or white color powder on the terminals of your battery because it’s a sign of corroded terminals. And, yes, corroded terminals are another sign that you have a dead battery.
  • Another direct and clear sign of dead batteries is a swollen battery. The reason behind a swollen battery is a faulty alternator. When the alternator overcharges the battery, this problem occurs.

How to Resolve The Issue

Let me speak honestly; there are a few things you can do about a dead battery but replacing it. It’s best to straight to a repair shop or auto parts store for a new battery.

But there are a few tricks you can follow until you’re getting a new car battery for your vehicle.

  • Try to jumpstart your vehicle; it should help the battery accept a charge. But make sure you don’t jumpstart the vehicle with a frozen battery because there are chances of explosions. First, thaw the battery and then attempt it.
  • Check the electrolyte level of your vehicle. If it’s low, add distilled water and fully submerge the plates. It will provide a bit more reaction area so your engine is able to take a couple of turns.

To prevent a drained battery, try to use a battery maintainer whenever you park the vehicle.

5. Extreme Weather

Your car battery is neither safe in extremely hot weather nor it’s safe at freezing temperatures. Both situations can damage the battery and here’s how.

  • If you overcharge your car battery, the extreme heat can lead the charging system components (e.g the voltage regulator) to malfunction.
  • Also, high temperature causes the internal lead plates of your battery to corrode which results in deterioration.
  • If the temperature is under 32℉, a car battery’s performance can drop by 20%. The percentage is even higher when the temperature is at minus degrees. For example, the battery can lose 50% of its capacity at -22℉.

How to Identify

You can identify the issues by inspecting the performance of your car battery. If you notice the charging components aren’t working properly and the weather is hot, chances are it’s the temperature.

Also, extremely low temperatures can thicken the engine oil which forces your car battery to work harder when turning over the engine. Another easy way to detect the problem is, car batteries recharge slower in low temperatures.

How to Resolve The Issue

If your car battery is too old, it’s more vulnerable to heat and cold. So, replace the battery if needed. Or if it’s relatively new, get the battery checked by a car mechanic. An experienced mechanic will detect the main issue and change the damaged parts.

To prevent the issue, make sure you park your vehicle in shade on summer days. But when it’s winter, find an indoor space to park your car so it’s protected from the freezing temperature outside.

6. Not Enough Time To Recharge

Lastly, there can be another reason why your battery keeps dying is that you’re not giving it enough time to recharge. If you start the car and turn it off again continuously, the alternator doesn’t get enough time to recharge the battery.

Frequent starts and stops draw a lot of current and reduce the charge in the battery. 

But taking too short trips doesn’t provide enough time for the alternator to restore that much charge. As a result, the battery ends up dead eventually.

Why Does Car Battery Keep Dying But Alternator Is Good infographic

What Are The Signs of a Bad Alternator?

Although you know that the alternator of your vehicle is in good shape, just double-check it for re-confirmation. The alternator is the component that recharges your battery, so, it must perform properly to keep your battery healthy.

Below are some signs of a bad alternator:

  • Malfunctioning accessories
  • Whining or growling noises
  • Overly bright or dim light
  • Engine stalling
  • The smell of burning wires or rubbers

So, if you notice these signs along with a consistently dead battery, the alternator is not in good shape. So, take action accordingly.

Frequently Asked Questions

1. Can a blown fuse be the reason for battery drainage? 

Well no, the power drain can’t only be caused by the fuse itself. It does, however, show where the drain on power is coming from. If you pull the fuse and the battery drain slows down noticeably, then there’s an issue with the circuit.

2. Is it possible that short wear is the reason for battery draining? 

In some situations, short circuits can cause a parasitic drain that drains the battery. Most of the time, the signs of a shortage of power or ground are the same as those of open circuits. Therefore, when you figure out that there have been issues with short wear you should look into the matter immediately. 

3. What drains your car battery most of the time? 

Problems with your car’s electrical system along with broken fuse, bad installation, and bad wiring can severely cause car battery drainage.  This drainage issue can also strike even when your car engine is turned off. Therefore, it’s essential that you maintain the car batteries on a regular basis for optimum performance.

Bottom Line 

As we can see, any of these could be the reason why the car battery keeps dying but alternator is good. You can follow up the steps to check which one is causing the battery to die in time and take necessary measures to prevent the battery from dying completely. 

Even the best alternator out there can not revive a dead battery. By being a little careful about the causes, you can avoid buying another expensive car battery.

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William Baldwin

This Is William Baldwin, The Founder & Managing Editor of this website. Me and my team share automotive tips, tricks, and news

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Talha Atta

Talha Atta, a Mechanical Engineer and experienced technical content writer and editor at Autoglobes.com with a passion for the automotive industry.