Hey, Why Is My Car Battery Leaking?

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Four common causes for a vehicle leaking red fluid and their related parts.
The battery is a chemical storage device that stores voltage for the vehicle's accessories. If for any reason, the battery is overused or underused, the chemicals in the battery can cause adverse effects on the internal components of the battery, causing it to wear or short out. When the battery is stressed, it can swell and cause the internal components to leak out. When a battery leaks, it can leak a clear liquid or develop corrosion that builds up around the battery and components around the battery.

Is Your Car's Battery Leaking?

The battery can leak by banging around if its hold-down rack is faulty.  However, the leak can also come from the terminals getting excess vibrations. Alternatively, if chemical reactions cause internal shorting, the battery can swell and crack.

Don't ignore a leaking car battery! This is a clear warning that your vehicle's roadworthiness is compromised, which could lead to unsafe conditions. It's time to take control and understand what's causing the problem and what you can do about it.

Don't let the problem build up. It's always a good idea to seek the advice of an experienced technician to help you diagnose and fix the issue. By addressing the car battery leak early on, you can avoid costly repairs, keep your vehicle in top shape, and have peace of mind knowing you're safe on the road.

Let's Get To The Bottom Of It!

  • Q: Does the battery appear to be wet?

    Inside a car battery, some plates or cells hold acid and create energy for the car. A plastic housing separates the acid to keep everything safe and prevent short circuits. But if the battery gets damaged, like in an accident, it can cause the plastic housing to crack, and the acid can spill out. So even if the battery is securely tight, the housing can still crack and cause an internal acid leak. As a result, the battery might look wet or sweaty on the outside.

  • Q: Is the battery looking bulged?

    If your car battery is sealed, but the suspension or motor mounts are wearing out and making the battery bang around, there might be problems. The plates inside the battery can get damaged and short-circuit. This results in gases building up inside the battery, bulging it like a balloon. This can be dangerous, so consider assistance if your battery is swelling.

  • Q: Can the battery freely slide around the battery tray?

    The "battery hold down" is like a large metal belt that holds the battery on its tray. However, it wears quickly over time since it's so close to the battery and the acid inside. When this happens, the hold-down can break, making the battery loosely slide around the tray. This can be dangerous as the battery might bump into engine components or cause an electrical short by bumping the wrong spots.

  • Q: Is the "check engine" light on the dashboard?

    Your car's computer is smart enough to monitor the battery temperature. It uses a particular sensor that tells how hot or cold the battery is. This helps the computer ensure the battery charges at just the right speed. However, if the sensor goes on the fritz and sends the wrong information, it can cause trouble. For example, if the sensor always says the battery is too hot, the computer might charge it too much. And if it always says the battery is too cold, it might not charge it up enough. When this happens, the "check engine" light will warn that something's wrong.

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Vehicle Health Inspection Proof

Explore the following typical inspection results that show a potential cause for the symptom and select the one you believe is similar to your vehicle's issue.

Defective battery hold-down

The proof image shows that the broken battery hold-down bolt allowed the battery to slide around.

When the customer dropped off their vehicle, they informed us that the battery hold-down bolt was broken and the battery was sliding around in the battery tray. The customer had tried to remove the bolt but couldn't, as it was seized in the metal part in front of the radiator, and nothing was sticking out to remove the broken-off bolt.

During the test drive, the technician didn't notice anything about the customer's concern. However, during the vehicle health inspection, the technician noticed that the front bolt into the radiator core support was broken. Consequently, the battery could slide back and forth.

The customer authorized additional tests to extract the bolt from the radiator core support. Then, the technician used a drill bit to drill out the center of the bolt and used an extractor to remove the bolt from the radiator core support.

Next, the technician secured the battery hold down with a new bolt. Additionally, the technician cleaned any remaining acid on the battery holder and sealed it with a battery sealing spray.

Does the issue look like this? if not accessible your shop will document it
Battery sensor failure

The proof image shows the location of the failed battery temperature sensor at the bottom of the battery box with the battery removed.

A customer dropped off their vehicle and reported that their headlights had been flickering and that the check engine light had been on for about a week; they thought these issues were related.

The technician noticed no headlight problems during the test drive but confirmed that the check engine light was on the dashboard.

After conducting a vehicle health inspection, the technician found no issues related to the customer's concerns. However, a diagnostic scan revealed that the battery temperature sensor circuit was registering as high.

Further diagnostics were authorized, and the technician used a specialized scanner to check the live data. By analyzing this real-time information, they found that the battery temperature sensor was registering -40 degrees, which is out of range.

Since the failed sensor required replacement, the technician first removed the battery to gain access to the sensor located in the battery tray. They then used an ohm meter to test the sensor and confirmed its malfunction. After rehabilitation, the vehicle was tested to ensure the new sensor was functioning correctly.

Does the issue look like this? if not accessible your shop will document it
Battery internally shorted because of leaks and seal issues

The proof image provided shows the damaged battery with an internal short. Replacing a swollen battery with an internal short is essential to avoid the risk of explosion or damage to other vehicle parts.

When the customer brought their vehicle to the shop, they reported that the engine was slow to start and, on one occasion, wouldn't start. They attempted to jump-start the car, but they noticed the battery bulged out, so they tow-rode to the shop.

After the technician used a jump box to start the vehicle and bring it into the shop, they conducted a vehicle health inspection. During the vehicle health inspection, the technician tested the battery and found an internal short, causing the battery to swell.

Based on the inspection findings, the technician recommended replacing the battery. Unfortunately, a swollen battery with an internal short cannot be repaired and must be replaced to ensure the proper functioning of the vehicle.

Finally, the customer was instructed to replace the battery, understanding what happens in a short circuit and what could happen if the battery leaked. Finally, once they approved, the technician replaced the battery with a new one. This will ensure that the vehicle will start properly and run smoothly.

Does the issue look like this? if not accessible your shop will document it
Alternator overcharging the battery, causing it to leak and triggering the check engine light

The proof image is a voltmeter reading showing that the alternator was charging at a high voltage, confirming the alternator or voltage regulator needs replacement.

The customer dropped off their vehicle because they had to replace the headlight bulbs more often than usual. The last time they replaced a bulb, they noticed that the battery was hot to the touch. The customer also mentioned that the battery light was on the dashboard. However, they thought it was a false alarm since the headlights still shone.

During a test drive, the technician confirmed that the battery light was on the dashboard, and all other dashboard and accessory lights were bright.

The technician then inspected the battery and noted a surface charge in it. Therefore, the surface must be discharged before the battery can be tested appropriately. Still, all vehicle lights were working correctly.

Using a digital voltmeter, the technician tested the alternator's charging voltage and found it over 18 volts, which is too high. In this case, the test result means that the voltage regulator inside the alternator was not functioning correctly, causing the alternator to produce too much voltage.

Finally, the alternator must be replaced to ensure the vehicle's electrical system operates properly.

Does the issue look like this? if not accessible your shop will document it
Cracked battery case

The proof image shows the crack in the battery casing that allowed liquid acid to leak out, causing corrosion and wetness on the front of the battery.

The customer was concerned that the car's battery appeared wet and had white crusty corrosion. However, the vehicle seemed to run fine, and the electricity-demanding accessories operated normally.

During the test drive, the technician found no problems related to the customer's concern.

During the vehicle health inspection, the technician noticed the battery had a white acidic crust and appeared wet. However, the battery passed the load test, which is a test to check the battery's ability to deliver power.

The technician wanted to investigate the issue further and removed the battery holder. They found that the battery case was cracked, and there was battery acid leaking. Acid had been leaking out, and the battery needed to be replaced to avoid further damage to the vehicle.

Does the issue look like this? if not accessible your shop will document it
Battery post seal leak allowing acidic chemicals to seep from the battery and create corrosion around the terminals

The proof image shows the corrosion on the battery cable ends caused by battery leakage on the lug seals. This quickly develops into many issues in the whole battery system.

A customer dropped off their vehicle complaining about a lot of green and white buildup around the battery cable terminals; it looked like a leak. They had attempted to wipe it off, but when they accidentally touched it with their forearm, they felt a burn.

During a test drive, the technician observed nothing related to the customer's concern. However, during a vehicle health inspection, they did notice that the battery cable ends were corroded with buildup.

The technician recommended removing the battery cables and cleaning them with a specific solution. They also installed battery terminal protectors under the cables and cleaned the battery lug and cable ends before tightening them. Finally, they would apply a battery cable sealing spray to the cables and lugs.

The technician recommended cleaning and protecting the battery cables to prevent further corrosion and ensure the vehicle's electrical system was functioning correctly. Leaking batteries are dangerous and toxic, so wear protective gear if you decide to investigate on your own.

Does the issue look like this? if not accessible your shop will document it

Typical Fixes to Address the Cause(s)

The following chapters bases themselves on experiences from our auto repair shop; we'll describe related problems' causes and fixes.

"Alternator Replacement" fixes "Alternator overcharging"

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Hey, Why Is My Car Battery Leaking?
Sometimes a problem is more challenging to describe than it initially looked like. If you are not sure your problem is described by this article, please find below similar vehicle symptoms, which might describe better the issue you are experiencing.

Other things your auto repair shop might talk about:

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