Car Battery Leaking From Top: Common Reasons and Fixes

A car battery leaking from top causes several issues from corroding metallic parts of the engine to the vehicle refusing to start. Thus, you need to attend to it immediately after you spot the leakage.

Car Battery Leaking From Top

However, there are many causes of the phenomenon and it’ll be difficult to go through them. Thus, we’ve compiled the most common causes that cut across most vehicles and will suggest the best ways to fix them in this guide.

What Causes Your Car Battery To Leak From the Top?

The common causes of your car battery leaking from the top are overcharging, old age, damaged battery, extreme temperatures, and wrong electrolyte level. Some leaking car battery symptoms include a rotten egg smell coming from the front of the car and a bulge from the side of the battery.

Also, you’ll notice some corrosion around the terminals and what looks like sweat trickling down the battery.

– The Number of Years the Battery Has Been Used

Old batteries tend to leak from the top because they are simply aged. Batteries, just like any other thing, don’t last forever; time catches up with them. If you’ve been using the same battery for the past three years, you should consider changing it even if it hasn’t started leaking from the top. The process is even hastened if the battery sits unused in the car for a very long time.

When a car battery remains unused in a car, it causes hydrogen to build up, which eventually breaks the battery seals. The hydrogen gas then escapes through the cracks on the seals but they are not alone; the acid in the battery also follows suit. The acid then destroys other parts of the vehicle it comes in contact with. Also, a bad battery shouldn’t remain idle in a car for a long period.

– Overcharging the Battery at a High Voltage

Another common reason a car battery will leak at the top is when you overcharge them, especially at a very high voltage. Overcharging a battery at a high voltage breaks down the battery acid, which becomes corrosive and eats away the battery plates.

If the battery is vented, then the corrosive liquid will escape through the vents and cause damage. However, if the battery is sealed then the pressure from the gas could force the battery to burst and leak its contents onto the engine and damage its parts.

– A Battery With a Crack Near/Around the Top

A battery that is broken near the top will certainly leak its constituents and cause damage. This usually happens when the car battery is not handled properly, causing it to fall and break. If the battery is also not placed properly on a shelf or level ground, it could fall on its head and get broken.

Causes of Car Battery Leaking From Top

Some objects can also fall on the battery during storage and depending on their weight, they’ll break the top of the battery, causing its constituents to leak.

– Overfilling the Battery Chambers With Water

Batteries that are not maintenance-free would require a constant filling of water to protect the active material in the battery and to generate power. When the water level goes down, the active material will oxidize and the car battery will lose its power.

However, if you have overfilled battery chambers with water, it’ll cause the battery acid to overexpand and overflow. When this happens, the battery begins to leak the mixture of the electrolyte and diluted water.

Moreover, the excess water can dilute the power generated by the electrolyte, resulting in reduced power output. Thus, we recommend you allow battery shops to fill your battery with water, but if you have to do it yourself, ensure you fill it to its correct level.

– Tipping a Partially Sealed Car Battery

Some batteries are not fully sealed because the chemical reaction between their constituents produces hydrogen gas that needs to flow out. Fully sealing the batteries won’t allow the hydrogen gas to escape, causing it to build up and finally explode.

Thus, these batteries have vents to allow the hydrogen gas to escape. Now, if these batteries are tipped, their constituents will begin to leak through the vents provided for the hydrogen gas.

– A Car Battery Suffering Sulfation

This is when lead sulfate crystals form on the surface and pores of the active material of the battery’s plates. This usually occurs when the batteries are frequently undercharged. If the sulfation continues for a while, it could cause the acid to boil over and spill out of the battery.

– Harsh Weather Conditions Affecting the Battery

Extreme temperatures take a toll on the lifespan of a battery and can also cause it to leak. In very frigid temperatures, the electrolyte will expand and then freeze. This action can result in the breaking of the battery cover and subsequent leaking of the electrolyte.

If the weather is too hot, the electrolyte could evaporate and compromise the internal structure of the battery. When the electrolyte leaks through evaporation, its level drops and becomes increasingly difficult to hold a charge. On a few occasions, the compromised internal structures could result in the direct leak of the electrolyte.

On the other hand, extreme cold weather can cause slow chemical reactions and condensation. The condensation can lead to battery corrosion and permanent damage to the battery. Sometimes, frigid temperatures can dilute the electrolyte.

How To Fix the Various Causes of Car Battery Leaks From Top

To fix the various causes of car battery leaks from the top, you can try using correct pulse charging techniques, removing the water from an overfilled battery, or tightening the battery terminals to stop the leakage. Make sure to figure out the problem before attempting to resolve it.

Some of the methods to fix some of the causes are simple, while others are a bit complicated and the rest just require a battery replacement. For example, there’s no other way to fix an old battery than to replace it with a new one. Also, all you have to do to fix a battery that leaks due to tilting is to place the battery on a leveled surface. Now, let’s look at how to repair the more complicated ones.

– An Efficient Way To Fix Car Battery Sulfation

A sulfated battery can be reversed by using correct pulse charging techniques. Interestingly, there are plenty of these techniques with some of them more technical than others. One of these techniques involves charging an already charged sulfated battery with a regulated current of 200mA. Allow the battery voltage to go up between 2.50 V/cell and 2.66 V/cell for about 24 hours.

Fixes of Car Battery Leaking From Top

To quicken the process of dissolving the crystals, you can raise the temperature of the battery to between 122 degrees Fahrenheit and 140 degrees Fahrenheit. However, if you allowed the sulfation to go on for weeks or even months, then you might need to replace the battery.

– Saving a Car Battery Overfilled With Water

Saving a car battery overfilled with distilled water must be done with utmost care to avoid damaging the battery components. One way to fix this is to take a straw and dip it into the water; this will trap some of the water within the straw. Now, place your finger at the end of the straw and then pull it out and spill the trapped water on the floor. Repeat this process until the level of water drops to the desired point.

A simpler method will be to purchase the syringe that is used to fill the car battery with water. The same syringe can also be used in drawing out the water, thus dip it into and allow the water to flow up the tube of the syringe, then spill the water onto the ground. Keep doing this until the water level drops.

– Tightening the Battery Terminals

When you first discover you have a leaking car battery, one of the first things you can do is to tighten the terminals to stop the leakage. You can also use sealants to keep or tapes to cover the cracks or holes that are causing the leak. Using sealants is a bit tricky and should be done with caution to avoid burns and corrosion.

First, pour out the battery fluid into a container and pour baking soda into the electrolyte in the container to neutralize it. Next, sand the area around the crack or hole until the area becomes smooth, and apply the sealant. Leave it to dry for about two hours and then recondition the electrolyte by adding three cups of distilled hot water, which should increase the temperature to around 150 degrees Fahrenheit.

Add a cup of Epsom salt to the distilled hot water and allow it to cool down completely before pouring it into the electrolyte. Now, fill the battery with the electrolyte, fix new caps, shake the battery and let it charge for about 36 hours before you use it.

To replace the battery, first remove the wires from the terminals and use a socket wrench to undo all the bolts holding the battery down. Take out the old battery from its compartment and clean the place if it is dirty. Place the new battery into the compartment and tighten the bolts that you initially removed. Reconnect the cables of the battery terminals in the reverse order in which you disconnected them.

Frequently Asked Questions

– How Do You Fix a Car Battery Leaking From Positive Terminal?

To fix a battery leaking acid from the positive terminal, you need to empty the battery and use a sealant to seal the leakage. Now, leave it to dry for about two hours then recondition the electrolyte, pour it into the battery and charge it for 36 hours.

– Can You Drive With A Leaking Car Battery?

No, you shouldn’t drive with a leaking car battery because it is not safe for the vehicle and the environment. Car batteries contain acid, which might corrode parts of the vehicle. In time, the vehicle will also fail to start because the battery can’t hold a charge.

Reasons and Fixes of Car Battery Leaking From Top

Can a Leaking Car Battery Cause Blue Smoke from the Exhaust?

A leaking car battery is not one of the top causes of blue smoke from the exhaust. Blue smoke usually occurs due to oil burning in the engine, indicating internal issues such as worn piston rings or valve seals. However, addressing battery leakages is crucial for overall vehicle safety and performance.


This article has covered the various reasons car batteries leak acid from the top and has suggested specific ways by which you can fix the leaks.

Here is a recap of all that we’ve discussed:

  • Car batteries can leak at the top for many reasons, but the most common ones include sulfation, cracked battery, tipped battery, and extreme temperatures.
  • Other causes of battery leakage include overcharging the battery, the age of the battery, and a battery that is overfilled with water.
  • In some cases, the battery can be repaired, but in other cases such as an old battery, extreme sulfation and harsh weather, the batteries will need replacement.
  • Remember that some repair methods such as sulfation and fixing cracks on the battery are a bit technical, thus don’t hesitate to contact a professional if you need help.
  • However, other methods such as removing excess water are quite simple and can be done by yourself in a few minutes.

Don’t drive with a leaking battery as the acid could damage some components of your car. Also, remember to wear protective gear whenever you’re working on the battery.

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