Is it Possible to Overcharge a Car Battery? How it Can Happen

One of the least commonly known vehicle-related issues is overcharging a car battery. Despite this, overcharging a car battery is a fairly common mistake.

This can easily be done by a do-it-yourself mechanic since battery changes and recharging are not usually very difficult tasks; however, mechanics can make this type of mistake too.

There are several ways a battery can be overcharged, and several minor to very dangerous consequences can result. Fixing a battery overcharging issue often means switching the entire battery for a new one since this issue has a high potential to ruin a battery altogether.

How Does a Car Battery Work?

Without going into too much detail, a car battery works when the compounds within the battery react with each other to create energy. Most normal batteries contain lead and lead dioxide plates with each batter cell that trigger a reaction when they interact with sulfuric acid.

This reaction ultimately produces electrons that produce electricity that power the devices in your car and provide the power needed to start. Understanding these reactions and the chemicals that make them work is important when discussing the consequences of overcharging.

How Can a Car Battery Be Overcharged?

There are several different ways in which a car battery can be overcharged. Most are fairly obvious and can sometimes be caught in time to avoid total battery replacement, but others are not as easy to diagnose.

Leaving it on a Battery Charger for Too Long

Many different automotive retail locations sell battery chargers. These can be helpful when your vehicle has been sitting for an extended time without being driven. Of course, it can also be helpful to have just in case any other situation comes up.

When it is time to use the charger, it is important to use it for the amount of time noted on the instructions. Leaving the battery charging for too long is a surefire way to overcharge it.

Improper Battery Charger Usage

Using just about anything improperly will always have the potential for at least something undesirable to happen. For a vehicle battery, hooking it up incorrectly, not reading the instructions on how to use it, or any other improper usage could result in overcharging, especially if it is your first time using one. 

Faulty Battery Charger

If you have a battery charger that you have used for years, the best thing to do is to keep it in working order so that you can avoid a faulty charger.

If you find that you have bought a charger, and it is acting strange or not working correctly, you should be able to find out whether it is covered by a warranty and rectify the problem with the manufacturer.

A manufacturing flaw is much less common than a tool that wears out and breaks, but both happen.

Alternator Problems

A vehicle’s alternator recharges the battery as the vehicle moves so that it does not go dead from using the radio, air conditioner, and other controls. When the alternator wears out, breaks, or fails altogether, it could cause battery overcharging. More often than not, a failed alternator will ultimately not allow the battery to recharge and will eventually lead to the vehicle losing power altogether.

Despite this, a failed alternator can have the opposite effect. Modern vehicles use many different sensors for just about anything, including a sensor on the alternator that prevents the battery from being overcharged. If this sensor fails, the alternator will not be able to shut off providing a charge.

Voltage Regulator Issues

A vehicle’s voltage regulator evens out the amount of charge being sent to the power supply. This means that when there is a spike in electricity, the voltage regulator helps prohibit too much voltage from reaching necessary components.

Similar to the alternator problems discussed above, a faulty voltage regulator can send too much charge to the battery.

What Happens if You Overcharge a Car Battery?

charging car battery

Overcharging a car battery rarely has severe safety consequences for you, but that risk is not zero. Additionally, when dealing with a component that creates energy and has an electrical current, it is always best to be cautious when doing anything with a car battery.

Battery Lifespan Decrease

The most obvious result that will come from overcharging a battery is the decrease in its lifespan. This can be seen in smaller electronic devices as well, such as phones and flashlights.

Consistently leaving a phone or flashlight plugged in and charging will decrease its ability to hold a charge. The same is true of a car battery.

Read More: When Should You Replace a Car Battery? Lifespan Explained

Dead Battery

Most things are manufactured to be as safe as possible, and car batteries are the same. Most batteries are designed to simply stop functioning when overcharging is detected.

This prevents anything dangerous from occurring since a battery contains corrosive chemicals and can produce power.

Read More: How Long Does it Take to Re-Charge a Dead Car Battery?

Battery Swelling and Melting

car battery swelling

Battery swelling and melting are much more common in older style batteries. Modern batteries are usually much safer, but this is not impossible with them either.

Battery swelling can occur as overcharging causes the chemical reactions within the battery to occur at a higher rate or a more numerous rate than the battery is designed to handle.

Melting occurs because these reactions and electricity passing through the battery also create heat. When too much energy passes through the battery, both could occur.

Battery Leaking

Battery leaking is one of the direct results of both swelling and melting. This is problematic since the chemical compounds that make up the battery are corrosive. Sulfuric acid is both toxic and harmful to the skin and the environment which is also why batteries should be recycled appropriately rather than being thrown away at the end of their life.

Battery Exploding

car battery explosion

In rare situations, a battery could explode. Again, this is more common with older battery types, but it is possible in any battery when overcharging occurs. This is especially true when bulging occurs since the contents become pressurized as excess energy is passed through the cells.

How Do You Check For and Fix an Overcharged Battery?

There are only two fixes for overcharging batteries. The first is not as much of a fix as it is a precaution: do not overcharge the battery.

Always read the instructions on any battery charger if that is what you are using that could cause overcharging. If a battery has been overcharged, there is still the chance that you can use it if it has not died. Doing this consistently will decrease its lifespan or cause other issues, but just because it has happened once does not always mean the battery is ruined.

The second fix for an overcharged battery is to replace it. If the battery melts, swells, or explodes, it is obvious that a replacement is necessary. If your vehicle’s alternator or voltage regulator is to blame for an overcharged battery, a fix for those components may accompany a battery replacement if the damage is too extensive for the battery.

To check for an appropriate battery charge, you can buy a multimeter to read the voltage through the battery. When your vehicle is on, you can use the multimeter on the battery terminals to see the amount of voltage traveling through the battery. Normal voltage is usually between 12.8 and 14.7 volts.

Final Thoughts

It is possible to overcharge your car battery. Overcharging from using a battery charger is easy to do if you are not careful to read the instructions.

This is easily fixable if you know what is happening by charging the battery for the appropriate time. Overcharging from other sources like a faulty alternator or voltage regulator are not always as easy to diagnose.

Overcharged batteries usually suffer from decreased lifespan or just die after too much charge is received. In extreme cases, overcharging can cause battery melting, swelling, and exploding. You can check your battery voltage by using a multimeter, or if you are uncomfortable doing so, you can have a mechanic do it for you.

Shawn Furman
I have been a vehicle hobbyist for as long as I can remember as well as a freelance writer for the past three and a half years. My clients have included Vehicle Scene, Autolist, CarGurus, and now The Vehicle Lab. In addition to my current clients, I also maintain my own blog where I am able to share my knowledge and experience through vehicle reviews, car-buying guides, how-to guides, and list articles.
The Vehicle Lab looks to cover all aspects of the automotive industry: News, Maintenance & Repair Guides, and Product Reviews
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