Informational Guide

Dead Cell In Car Battery (Signs, Symptoms & How To Fix)

Car batteries use science to hold their charge, but sometimes it needs help. We look at what it means to have a dead cell in a car battery & how to fix it.

Without a good automotive battery, you can plan on running into plenty of problems, especially when you are already running late. By understanding the symptoms of a failing battery, you prevent a lot of headaches.

In this guide, we look at what it means to have a dead cell in a car battery and how to fix a car battery with a dead cell.

The car battery is considered a wet cell design. Each battery contains six cells filled with lead alloy plates and a sulfuric acid solution, known as the electrolyte.

Each cell will produce about two volts of energy, creating the 12-volt battery. The sulfuric acid triggers a chemical reaction between the plates, causing it to produce lead sulfate and ions.

These ions then go on to have a chemical reaction with the plate and produce hydrogen that turns into electrons. As the electrons race across the plates, electricity is generated, which is the power needed to start and run your car.

Dead Cell In Car Battery

What Causes A Dead Cell in a Car Battery?

Can a dead cell in a car battery be fixed? It depends on what causes a dead cell in a car battery. Here are a few known causes


When the car battery isn’t being used regularly, the substance created by the acid and plates sits inside the case. It starts to harden on the plates and leads to sulfation. The longer it sits without recharging, the more of a problem this becomes.

Age of the battery

Over time, the cells will run out of chemicals needed to continue the process. Old battery cells are also subject to shorts, and erosion can occur due to age. To prevent this, it's important to replace the battery as it gets older.


Corrosion occurs from overcharging and undercharging the battery. Both of these conditions also decrease the battery life overall. As the battery ages, corrosion becomes more of a factor. Thankfully, it is possible to clean off the corrosion, which also produces a better connection.

Electronic parasites

Many things are drawing power from your battery. If they aren't kept in check, it could lead to dead battery cells. Bad alternators, faulty circuits, and loose terminals should all be repaired to ensure optimal battery health.

Dead Cell In Car Battery: Common Signs

The symptoms of a dead cell in a car battery aren’t difficult to spot. Here are some of the most common dead cell in car battery symptoms to look for.

Slow to Start

When you turn the key and the engine tries to crank but it takes a while, it could be a sign that a battery cell is dead. As time goes on, you might notice that process takes longer and longer.

Cranks, but doesn’t start

If you hear cranking or just a click but the car engine won’t start, it’s likely either a dead battery cell or a defective alternator. If it’s the battery, a quick jump start should get you down the road to replace it.

Dim Lights

As the car battery fails, you will notice the lights starting to get dimmer. This occurs with both the headlights and the lights on your dashboard.


As the battery ages and starts to fail, you might notice more corrosion on the terminals. You can learn how to clean car battery corrosion, but that won’t change anything if it is already failing.

Battery Light Comes On

In modern vehicles, cars come equipped with tons of dashboard lights to alert you to any problems. One such light you want to look for is the battery light, indicating trouble with the charging system.

How To Test A Car Battery For A Dead Cell: (Mechanics Guide)

Before you learn how to fix a dead cell in a car battery, you must first figure out how to test a car battery for a dead cell. Our guide will walk you through the process.

Inspect the Battery

Your first step is to inspect the battery. You are looking for a broken terminal, crack in the plastic, bulging case, excessive leaking, or any discoloration that might lead you to believe there is a problem.

Take a Voltage Reading

With your voltmeter, you can check the battery health. Here’s a handy chart that you can follow.

Voltage Level

Percentage Charge


100 %




75 %


60 %






25 %


No charge, 0 %

Load Test the Battery

You can do your own load test with a voltmeter, but the battery must be fully charged. You may also need a friend to help.

  • Hold the voltmeter to the terminals of the battery.
  • Try and start the vehicle and watch your voltmeter readings.

A healthy 12-volt battery should maintain a reading above 9.5 volts while under a load. If it holds but then starts to drop, there is an issue. Most likely, there’s a dead cell.

How To Test Car Battery For Dead Cell

How To Fix A Dead Cell In A Car Battery

Do you know how to fix a dead car battery cell, or do you need to learn how to replace a dead cell in a car battery? In some cases, it’s possible to recondition the car battery and get some more life out of it. However, this only works with some car battery types and requires a few supplies, such as distilled water and Epsom salts.

If you are unable to figure out how to fix a dead cell in a car battery, you are only left with the option to replace the car battery.

Battery reconditioning will help you learn how to revive a dead car battery cell in many cases, but it won’t fix the problem forever. While you might be able to temporarily learn how to recharge a car battery with a dead cell, eventually, you will need to replace it.

People Also Ask (FAQs)

Can a completely dead battery be recharged?

If the battery recently died, you might be able to use a deep cycle battery charger to get it going again. However, most dead batteries are going to require a replacement because they are nearly impossible to bring back to life, especially if they have been sitting for a long time.

How long can a car battery stay dead?

You can leave a fully charged car battery sit for about two weeks without using it and still be able to get it going. However, letting it sit beyond this time could cause it to die without any chance of revival.

How many volts should a car battery lose overnight?

The parasitic draw on a car battery should never equal more than 50mA. If you are losing an excessive amount of voltage, you might want to have the electrical system checked before it kills the car battery.

How many volts should a battery have?

When the car battery is fully charged, it should contain 12.6 to 12.8 volts. If you are trying to figure out how many volts is a car battery, you can use the voltmeter to get the reading. If the reading is much lower than this, it might not start.


Now that we have looked at what causes these problems and how to fix a dead cell on a car battery, you are ready to take charge of the automotive battery health. Ensure you are never left stranded again by caring for your car battery.