Why Is My Car Battery Leaking From The Top?

A lead-acid battery contains two plates – a lead peroxide plate and a sponge lead plate. Both are dipped in a mixture of sulfuric acid and water. A chemical reaction takes place to produce the electricity required to make the battery work efficiently.  

One of the many defects that car batteries experience is leaking from the top. This happens in units that have some form of damage or wear and tear. The sulfuric acid or water can always be seen from the top of the battery.

The good news is that hardly do car batteries leak. But when they do, it’s always best to address the problem immediately. In this guide, you’ll understand what causes leaking in car batteries, the signs and symptoms to watch out for, and what to do when it happens.

What causes a car battery to leak from the top?

·       Wear and tear

A lot of times, leaking occurs in very old car batteries. The average lifespan of a new battery is about 4 years. Most units are designed to last up to 5 years. They deteriorate with time until they are no longer able to produce the power needed to start the engine.

Batteries undergo several cycles of charging and discharging. The active materials are subjected to a lot of motion to help release the electricity stored. With every cycle, a small amount of active materials are lost.

One of the main factors that determine how long a battery will last is the vehicle’s usage pattern. This affects the rate at which your battery will age. In addition to leaking, you’re likely to experience other problems such as dimming headlights and other electrical issues.

·       Damage

A car battery could be leaking from the top due to physical damage caused by an accident or excessive shaking. This can lead to cracks that allow the electrolyte to seep through. You’ll typically see the fluid flowing from the damaged area.

·       Overcharging

A faulty alternator regulator can cause the alternator voltage control circuit to fail. This then causes the battery to overcharge. When this happens, the electrolyte boils and flows out of the vent caps. You may notice that the car battery leaking from the positive terminal.

It leaves the unit covered in moisture. It’s important to pay attention to a car battery that is leaking fluid when charging. It may be characterized by a black coating on the filler plugs, a strong smell, and a low acid level.

A smart battery charger can help keep an eye on your car’s battery and prevent it from overcharging. The thermal sensor helps to prevent undercharging in cold weather and overcharging in hot weather.

·       Overfilled battery

Older versions of lead-acid batteries need to be occasionally filled with water. This is because during normal operation, they only consume the water and not the sulfuric acid. The water gets converted into hydrogen and oxygen as the electricity flows.

This causes the electrolyte/fluid to run low. Car owners are required to refill the car battery with distilled water to keep it healthy and safe for use. However, overfilling can cause the battery to leak from the top.

According to NorthEast Battery which manufacturers several battery brands, the water level should be about ½ an inch above the top of the plates. Only add water when the battery is fully charged. Otherwise, you run the risk of electrolyte overflow.

It’s good to note that most cars today feature a maintenance-free battery. This is a sealed battery that prevents fluid leakage or loss. It does not require the addition of distilled water. The escaping gases recombine into water and drop back into the battery.

·       Sulfation

Sulfation occurs when sulfate crystals build up on the plates. It happens when a battery is left discharged for a long period of time. A chemical reaction leaves a non-metallic luster on the negative plate and a grey/white coating on the positive plate.

This shortens the life of the battery, impairs its performance, and makes it unserviceable. Excessive sulfation also increases the chance of sulfuric acid boiling over. This is a major cause for a car battery to leak from the top.

·       Temperature fluctuations

Excessive heat created by a running engine or overcharging can cause the battery plates to expand. This then causes the electrolyte solution to be pushed out. It can be seen leaking from the top of the car battery.

On the other hand, extremely cold weather can cause the electrolyte to freeze. This creates pressure on the battery cells which end up pushing the casing outwards. As a result, the body of the battery may crack and leak acid.

·       Tipped battery

A car battery that is installed incorrectly inside the engine bay can also leak. If it does not sit flat on the surface, the sulfuric acid can spill over from the cells and from the top of the battery. Ensure that your battery is mounted at the right angle and not tipped over.

What Does a Leaking Car Battery Look Like?

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·       Corrosion

Sulfuric acid is corrosive. It eats away at the battery’s metal parts, causing them to corrode. Rusty terminals and cables are one of the most common signs of a leaking battery. They are characterized by a blue, green, white, or brown residue.

The residue causes electricity to flow less efficiently and leads to a decrease in battery power. Less current will flow, causing problems when starting the engine or when operating other electricals inside the vehicle.

·       Moisture on the battery

As mentioned earlier, overcharging can cause the battery to overheat. This causes the electrolyte to boil and vent out in form of steam. Once the steam has condensed on the battery casing, it forms droplets that indicate leaking. The battery looks like it’s “sweating.”

·       Low fluid

A decrease in the electrolyte level is another sign that you have a car battery that is leaking from the top. This is especially if it is due to something else other than a drop in water level. Check for a bubbly liquid that could be seeping through the vent cap.

·       Cracked or warped battery

Cracking or warping could be a sign of physical damage caused by an accident or impact from the vehicle’s movement. It’s common where batteries are not firmly mounted to the engine bay.

·       Faulty cell cap seals

Battery vent cap seals keep the electrolyte within the cells. The cap seals are vented to release pressure from the cells when gases form during charging.

This is done at a specific configuration to provide the appropriate venting pressure. Pressure ranges between 2 psi and 35 psi. If the vent caps fail, they can cause an increase in electrolyte leakage.

Damaged cell cap seals also make it hard to check the acid and water levels inside your battery.

·       Rotten egg smell

If you notice the smell of rotten eggs coming from under the hood, it could be a sign that your car battery is leaking from the top. Old dying batteries will often produce hydrogen sulfide gas which smells like well water, a sewer, or rotten eggs.

It’s good to note that hydrogen sulfide can irritate the throat, eyes, nose, and respiratory system. A car battery that stinks indicates that it’s time to change it. The unpleasant odor is toxic and can be harmful in high concentration.

How to fix a leaking car battery

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What you may need:

  • A 10-mm wrench
  • Gloves
  • Baking soda
  • Wire brush

There are different ways you can fix a leaking car battery depending on what is causing the leaking. If the battery is physically damaged, a silicone adhesive such as CRC RTV sealant can help patch up the cracked or warped area.

Master Bond epoxy is also a great alternative. Both are acid-resistant. Use a polypropylene piece of plastic to patch the area, like this guy. Be careful when handling a damaged battery as it is a safety and health hazard.

Avoid getting into direct contact with the acid. Transfer all the electrolyte from the battery into a plastic container before working on it. Wear gloves and use a solution of baking soda and water to clean the battery before working on it.

Baking soda neutralizes the acid. Use the same solution to clean the battery terminals if they are corroded. Scrub the gunk off using a wire brush. When applying sealant to cracked areas, allow it to dry for a minimum of two hours before touching it. Follow the recommended steps to recondition the battery.

While you may be able to fix a leaking battery yourself, the best solution is to have it replaced by a certified mechanic. A new one will cost you between $45 and $200 depending on the size, quality, and power. Visit the nearest automotive service center or auto parts store for a replacement.

How to dispose a leaking car battery

Fortunately, the materials used to make batteries can be reused to make new batteries as well as other items. If your car battery is leaking and you’d like to dispose it, there are different ways you can do that safely.

The most important thing to note is that lead-acid batteries should not be thrown in the trash. They are classified as toxic waste by the United States Environmental Protection Agency. They are harmful to human beings, animals, and the environment when mishandled.

You can get fined heavily for throwing away your battery carelessly. Some of the places you can take your leaking battery include:

  1. At the retailer that sold it to you
  2. An auto parts store
  3. The National Automotive Parts Association (NAPA)
  4. A local recycling center
  5. An Authorized Treatment Facility (ATF)
  6. Scrap metal yard
  7. Battery Collection Event

On That Note

A leaking battery is not something that should be ignored. Batteries help to turn the engine on and keep it running. They link the entire vehicle’s electrical system and turn its security features on. When something goes wrong with your car battery, your car will not function properly. This makes it necessary to get a replacement quickly to prevent any further damages.

Frequently Asked Questions

Is it safe to drive with a leaking car battery?

No. Exposure to sulfuric acid can cause tightness in your chest and difficulty breathing. The fumes are toxic and can cause dizziness or nausea. The best solution is to buy a new car battery if you notice the old one is leaking from the top.

Sulfuric acid is also corrosive and causes damage to metal parts inside the engine bay. Once it oxidizes, it starts to eat away at any components that it comes into contact with. If it leaks onto critical components and stays there long enough, it may cause permanent damage.

Can a leaking car battery explode?

A lead-acid battery undergoes chemical reactions that produce hydrogen gas. The battery is slightly unsealed to allow the gas to vent out. This is because it is highly flammable and very volatile.

It can cause an explosion if exposed to a flame or high temperatures, putting you and your car at great risk. This can happen when trying to jump-start a car battery that is leaking. The sparks could ignite the gas.

Old batteries also leak hazardous materials that are a fire risk. They can explode when exposed to strong electrical current or high heat.

What happens if you touch dry battery acid?

Contact with battery acid can cause pain, burning, itching, or redness. Exposure should be treated immediately. Flush lukewarm water on the affected area for about 30 minutes until the irritation stops. Seek medical attention if you experience severe burns.

Is the white powder from batteries harmful?

No. The white powder forms when potassium hydroxide leaks out and reacts with carbon dioxide in the air to form potassium carbonate. It’s common in batteries that discharge slowly over time. It is not harmful but any remaining potassium hydroxide should not be handled directly.