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Is It Safe To Drive a Car With a Leaking Battery?

Car with lead acid battery corrosion visible on the battery itself both terminals

There are a lot of things that can go wrong with your car, but how are you supposed to know how serious the problem is? I have friends who assume that as long as the car turns on correctly, it’s safe to drive. If your car battery is leaking, is this still the case?

It is not safe to drive a vehicle with a leaking car battery. A leaking car battery can explode, cause a fire, melt metal components under the hood, and kill you just from the fumes alone. The moment you spot a leaking battery, you should either replace it immediately or call a mechanic and have your car towed to their shop.

In this quick guide, I’ll be talking about leaking car batteries. I’ll discuss the science behind the leak, how dangerous it is, and whether or not it’s safe to drive a car with a leaking battery.

Quick Description: How Your Car Battery Works

You might take your car’s battery for granted, but there’s a lot of great science going on within its walls. To generate power, electrons need to move.

A power outlet in your home essentially has a ton of electrons that want to get going. You plug in your toaster, the electrons surge from the outlet into the toaster, and the bread turns into toast. With your car, this process needs to happen without a supply from your home.

Your car battery achieves this by using lead, lead dioxide, and some sulfuric acid to speed up the process. The combination of the three will force electrons to pass through your battery, and then the electrons go around your car to power different electronics.

Lead and lead dioxide are dangerous heavy metals and can lead to poisoning, but the real danger here is sulfuric acid. This acid will eat almost anything in its way.

When your car battery leaks, it’s the acid that’s getting away. It can start disintegrating components it comes in contact with and can melt your hand if you touch it (and if the acid’s concentrated enough).

Battery acid can dissolve asphalt, limestone, body parts, water, some plastics, and most metals. Notably, when it reacts with water and metal at the same time, flammable gas is created which can explode. If you’ve seen the video of a phone battery getting stabbed and then blowing up, that’s exactly what’s happening here.

This is the heart of why I made this blog post: battery acid is very dangerous.

Car battery cut with the lithium ion cells visible inside isolated against a white background

What Causes a Leaking Battery

Next, you might want to know why a battery would leak in the first place. Surprisingly enough, there are a few reasons why a battery might leak.

The Case Was Damaged

One of the most dangerous conditions is if the case of your battery was damaged. This might happen if a part broke in your engine compartment and hit the battery. It could also happen if a tool smashes into the battery while repairs are done elsewhere in the car.

Finally, a battery case could get damaged during the storage, handling, or transportation of the battery.

In any of these cases, you’ll notice acid leaking near the damaged part of the case. This can get tricky, especially if the damage occurs on a wall of the case that’s hard to see from outside the car.

Natural Vibration While Driving

Car batteries naturally have a shelf life before you need to replace them. One of the reasons why this is the case is because of the vibration that happens while driving.

The engine is going through dozens of small, controlled explosions every second. This will generate a lot of vibration, even with added dampeners and vibration isolators. Add in the fact that you’re driving over bumpy roads and hitting potholes.

Over time, vibrations will wear down your car’s battery. Since the case is only made out of plastic, it doesn’t take much to jostle a battery to fail.

What typically happens in this scenario is that your car battery has a tiny crack in it — maybe one that’s so small you can’t even see it. Over time, the vibrations will propagate the crack, making it longer and bigger. Eventually, the crack will be so large that it forms leak points for battery acid.

Fun fact: this is the same theory in physics that explains why bridges have to be replaced after a certain period of time. Vibrations from cars driving over the bridge propagate tiny cracks in the concrete, eventually leading to failure.

Car driving on a bumpy road with pot holes in the asphalt during winter season

Damage or Corrosion to the Terminals

Corroded terminals are a more common issue, but they aren’t as dangerous on paper. This naturally happens as batteries operate over time, especially if there’s a little bit of moisture that seeps in.

Corrosion alone will slow the flow of electricity and might lead to some reliability issues with your car. But that’s not it.

The problem is that corrosion to the terminals will also weaken the plastic and seal points at the terminals. This vulnerability could break via vibrations or damage to the battery. Since it’s weaker, it has a higher chance of failing and letting acid spill out.

Close up of a car battery with lead acid corrosion forming on the terminal

Battery Was Overcharged

If your battery goes flat and you charge it, it’s very important not to overcharge it. I didn’t know this fact until I worked on a car with an overcharged battery.

Charging a car activates the sulfuric acid and electron exchange between lead cells in the battery. A byproduct of this reaction is hydrogen sulfide. It doesn’t matter if you know what this chemical is, the big takeaway is that it’s a gas.

As more gas is created, pressure starts to build in your battery. With enough pressure, the battery’s case will start to bulge out and can even explode. After recharging your battery, look at the top and side of the case. If there is any bulging at all, don’t even turn on your car, call a mechanic and ask for a tow truck.

How to Spot a Leaking Car Battery

A lot of people don’t notice a leaking car battery unless they look under their car after it’s been parked for a while.

If a battery were sitting on a table in front of you, it would be immediately obvious that there was a leak. The problem is that an installed battery tends to be covered and hard to get a good visual on all six sides. There could be a crack on the bottom that you would never notice unless you pull the battery out.

Pop the hood and look at your battery. If it’s warped, bloated, or has severe battery acid corrosion, you could have a leak. Alternatively, if you smell something rotten, that could be sulfuric acid.

If the battery looks wet or like it’s sweating, that’s another indicator that there could be a leak.

Or use this quick cheat sheet. This is how to spot a leaking car battery:

  • The battery is swollen, bloated, or warped
  • The battery is wet, sweating, or there’s condensation
  • The battery smells rotten
  • The terminals are corroded or wet
Old car battery with a lead acid leaking problem with the terminals rusted corroded leaking and oxidized

Is It Safe to Drive a Car with a Leaking Battery?

After reading one of my previous sections that talked about how battery acid can cause an explosion, you probably guessed the answer to this question. Is it safe to drive a car with a leaking battery? Absolutely not. There is no condition where you should continue driving your car after spotting a leaking car battery.

At the least, the acid will drip on the road and start dissolving pieces that can turn into potholes. It will eat away at the floor of your garage.

In the most extreme case, the battery acid will react with the metal in the engine bay and cause an explosion. Another extreme example is the severe and long-lasting damage done to your body if you contact the acid.

Simply just inhaling heated sulfuric acid can cause death, difficulty breathing, and internal burns.

Do not drive your car if you notice a leaking battery.

Car battery fire damage with the engine and everything including the battery visibily melted
Fire damage caused by a leaking car battery

What if the Car Safely Turns on, Though?

Even if the car turns on, it’s not safe to drive around with a leaking battery. As your car draws on the battery, the inside of the battery heats up. This makes the chemical reaction more volatile and can cause an explosion even though the battery started safely.

Also, it’s just a matter of time before the leak gets so bad that your car won’t run anymore. When your car battery dies while driving, you’re in an unsafe position. It’s better to just get the car towed and have a mechanic deal with it.

How to Fix a Leaking Car Battery

In almost every case, the best option is to simply replace your battery. Trying to patch a hole in plastic that has caustic acid coming out of it is just too dangerous.

Personally, I don’t like dealing with leaking car batteries. This is a type of repair that I rely on mechanics for. Maybe it’s just me, but I’d like to stay as far away from battery acid as possible.

With that being said, the best way to fix a leaking car battery is to simply replace it instead of trying to clean it up and hoping that it doesn’t leak again.

Auto mechanic installing, removing, or replacing the car battery inside the engine bay

Conclusion

As you just learned (repeatedly), it’s not safe to drive a car if the battery is leaking. I suggest that you call a mechanic, have your car towed, and allow them to replace the battery for you. A leaking car battery can cause massive damage to your car or even take your life if you don’t treat it seriously.

If you want to learn more about your car, explore the rest of my site. I have a lot of content and questions to major car questions. Be sure to see what car products I highly recommend, and leave a comment below if this guide helped you at all.

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Ernest Martynyuk

An automotive enthusiast who's been tinkering with vehicles since I was 15-years old. Repairing automotive electronics has been my main job for over a decade now and have a passion for everything technical regarding cars.

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