How to Clean Battery Corrosion (and What Causes It). 12v car battery terminals

Safe charging of car batteries

Charging car batteries? Is it really necessary? If so, how often and for how long? Aren’t modern batteries maintenance-free? Many drivers have asked these or similar questions. Firstly: normally the alternator should adequately charge the battery in everyday use. However, there are situations in which recharging and other care can have a positive effect on the life of a car battery. For example, this is advisable for the use of conventional lead-acid batteries in combination with short journeys, especially in cold weather. The same applies if the vehicle stands in the garage for a long period.

Modern, maintenance-free batteries have the advantage that it is no longer necessary to top them up with distilled water. In order for a car battery to perform reliably, a good charge level can be ensured by the use of car battery charger.

DIY maintenance and battery charging – what to note

Important: Care is essential when handling lead-acid accumulators. With incorrect handling, the electrolyte in a starter battery can escape or splash. Overcharging can produce explosive hydrogen. If an older vehicle is not equipped with a maintenance-free battery a visit to a workshop is recommended.

Important: Regardless of this, protective glasses and gloves should be worn when servicing, removing or installing the battery. To prevent short circuits, it is essential to avoid connection of the terminals by contact with metallic or conductive materials, as otherwise there is a danger of electric shock or physical injury.

However, with proper and careful handling, all drivers can charge the battery themselves.

First of all: Preparation before starting charging

Charging of the battery in the vehicle is simpler and is preferable for safety reasons, although this is not always possible. If no garage or an electricity connection is available, there is often no alternative to charging the battery outside of the vehicle. Ensure good ventilation when charging in enclosed spaces. If the battery is removed from the engine compartment for charging, a second person should help to lift large batteries due to the heavy weight.

Important: With lead-acid batteries, the formation of explosive hydrogen and de-gassing must be expected during charging. In extreme cases, a high concentration of hydrogen may result in an explosion with serious injuries and damage.

Defects of the battery should also be noted. Acid may leak from damaged batteries. Physical contact with battery acid can cause serious burns. The affected area must be thoroughly rinsed with clean water and a physician must be consulted immediately.

Car battery charging – step-by-step

Important: The cable which is connected to the negative terminal must be disconnected first. This prevents a short circuit between the positive terminal and ground. Then disconnect the red cable which is connected to the positive terminal.

For lead-acid batteries which are not maintenance-free, we recommend that you visit a workshop. Under no circumstances should you check the acid-water level yourself.

With maintenance-free batteries, checking of the electrolyte is not necessary. Here, only the dirt needs to be cleaned from the vent pipes.

Regardless of the reason for charging (for example in the case of a dead battery, long standstill times, short journeys), it is advisable to have a battery test carried out by a workshop from time to time. This is the only way to ensure that your car will always start. According to the German ADAC, more than 46 percent of all breakdowns are caused by poorly maintained batteries.

Important: If the battery has to be removed from the car for charging, care must be taken to keep the battery upright when lifting and carrying it. If the battery is to be charged in the vehicle, all electrical consumers must be switched off before connecting the charger.

Important: The charger must be connected to the battery before it is connected to the mains. To connect the charger to the battery, first fasten the red cable to the positive terminal of the battery. Then connect the black cable to the negative terminal.

Important: The next procedure depends on the type of battery. To select the correct operating mode, the user should follow the information in the operating instructions for the charging device.

After the end of the charging process, the charger is first disconnected from the mains before the cables are disconnected from the battery. When installing the battery in the vehicle, the red cable must first be connected to the positive terminal. Then, the black negative cable is connected to the negative terminal.

Charging of a battery with EFB or AGM technology is identical, however, care must be taken that the device is suitable for batteries with start-stop technology. In this case, the information in the operating instructions should be followed.

Interesting facts about chargers and charging times

Many high quality chargers are compatible with various types of battery and switch off automatically when charging is complete. Intelligent chargers gradually shut down as the charge level increases and limit the current automatically. In this way, a good sate of charge can be ensured even with long standstill times and low outside temperatures. In case of doubt, consult the description of use by the manufacturer of the device. Proper and regular use of battery chargers can therefore increase the reliability and the service life of the battery.

Even though there is no risk of overcharging with the use of a high quality charger, the battery should not remain connected to the charger for more than 24 hours. A full charge is usually achieved by charging overnight.

In maintenance mode, batteries can be kept at a high charge level even with long vehicle standstill times. Even after a deep discharge, some chargers enable at least partial reconditioning of the battery.

Important: Even though the connection and operation of the charger is not complicated, several points should be noted. Charging a car battery differs in several respects from the charging of a conventional battery. The operating instructions for the charger provide all the necessary information.

How to Clean Battery Corrosion (and What Causes It)

Don’t be shocked if you lift the hood of your car and catch sight of some corrosion around your battery terminals. Battery corrosion is a normal part of battery life that can be caused by typical wear and tear. But just because it’s normal doesn’t mean you should ignore it. In fact, corroded battery terminals are a common cause of reduced battery life and electrical problems in vehicles.

Why? According to the Universal Technical Institute, “Corrosion on or around your battery’s surfaces can lead to increased resistance within the circuit, which can disrupt the electrical current.”

Not only will this shorten the lifespan of your battery, but it also can cause damage to the electrical systems within your vehicle. Keep reading for a step-by-step guide on how to clean battery corrosion.

What Is Battery Corrosion?

What is corrosion and how do you know if your battery has it? As your battery runs, the sulfuric acid releases hydrogen gas. The gas then mixes with the air around it. The chemical reaction that takes place as hydrogen gas collides with the air, moisture and salt causes corrosion.

Corrosion is fairly easy to spot: It’s a white, blue or greenish powder typically surrounding one of the battery terminals, posts or cables. It has a granular, powdery texture.

What Causes Battery Corrosion?

Car battery corrosion can happen for a number of reasons. In addition to the normal release of hydrogen gas, some of the most common causes of corrosion are:

  • Age. Car batteries typically have a lifespan of three to five years. They become more susceptible to corrosion as they reach their expiration date.
  • Overheating. Batteries that are overcharged or overheat due to higher temperatures are more likely to develop corrosion. That’s why corrosion risk is highest in the summer.
  • Leaking fluid. If your battery is cracked or damaged, battery acid can leak from the casing and cause corrosion around the battery terminals.

How to Clean Battery Corrosion: Step-by-Step

Step 1: Start with safety. The powdery buildup around your battery’s terminals is caustic and can damage your skin and eyes. Wear heavy-duty gloves and eye protection while handling battery corrosion, and immediately wash away any corrosive material that gets on skin or clothing.

Step 2: Disconnect the battery. Starting with the negative terminal, carefully release the cable from the battery. Safely position the cable away from the terminal, these things are built to deliver the cable directly to the battery and are susceptible to ‘slipping’ back into place. Next remove the positive terminal connection.

Pro Tip: Before disconnecting your battery, use a battery memory saver to save stored data and protect your car’s electrical system. Be sure to reference your vehicle’s owner’s manual for specific information on using a battery memory saver.

Step 3: Inspect the battery cables. Once the battery is disconnected, take a moment to inspect the cables. Is there fraying or corrosion where the cable connects to the terminal? Is the insulation dry or cracking? Damaged cables need to be replaced.

clean, battery, corrosion, causes

Step 4: Remove the battery from the vehicle. It’s possible to clean corrosion from a battery while it’s still in the vehicle, but the safest method for you, your battery and your vehicle is to remove it from the car and place it in a shallow bucket or pan to collect the corrosive material you’ll be washing away.

Step 5: Start cleaning. Now it’s time to neutralize and remove the car battery corrosion. Use a wire brush or scraper to remove any solid, powdery corrosion from around the terminals and dirt from the top of the battery casing. Brush the corrosion away and let it fall into the pan below.

Step 6: Neutralize. You have a couple of options to fully remove and neutralize the remaining corrosion:

clean, battery, corrosion, causes
  • Battery terminal cleaner is a commercially available product designed to clean and neutralize corrosion from your battery. It’s a spray-on solution that changes color as it reacts with corrosion.
  • Baking soda and warm water make for a good neutralizing solution to clean battery corrosion. Make sure to mix your solution, dip a rag and wipe corrosion away rather than dumping the solution over the battery top. This is to prevent solution from leaking into the battery cells and neutralizing the sulfuric acid inside.

Pro Tip: Don’t forget to clean the terminal ends that connect your battery to the cables. You can dip the ends in baking soda and water solution, or use a commercial battery terminal cleaner.

Step 7: Dry and polish. Using a microfiber cloth, dry the battery casing, posts and terminals. Use a terminal cleaning brush to remove any debris or coating from the terminals that may interfere with the connection.

Step 8: Replace and reconnect. Return the battery to its tray inside your engine and reconnect the terminals. This time, start by securely attaching the positive terminal to the cable, then finish with the negative terminal. Replace the battery hold downs.

How to Prevent Battery Terminal Corrosion

While corrosion is a normal occurrence, there are steps you can take to prevent or slow it.

Protect. After a thorough cleaning, coat your battery terminals with dielectric grease or battery terminal protector. Apply a healthy coat to prevent corrosion in the future.

Avoid under or overcharging. If you notice corrosion on your battery’s positive terminal, it’s a sign that your battery may be overcharging, which can be due to a faulty voltage regulator.

Corrosion that appears on the negative battery terminal is a symptom of undercharging. This can happen if you’re taking short drives and your electronic system is drawing a significant amount of battery power for onboard electronics.

In either case, it’s a good idea to bring your vehicle in on a regular basis to check for electrical faults.Routine maintenance on all systems — including your car’s electricals — is important for the health and longevity of your vehicle. A trusted technician can help keep your car on the road for years to come.

This content is for educational purposes only, please reference your product manual for specific information.

How To Clean Car Battery Terminals

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Table of Contents

Whether it’s a sleek new EV or an audacious 1960s Mustang Mach 1, most vehicles on the road today sport a 12V lead-acid battery. All modern cars rely on these lower-voltage systems to supply energy to various vehicular systems and accessories, including the stereo, headlights, power seats and onboard computers if so equipped.

But unlike contemporary lithium-ion battery packs used in everything from laptops to Tesla Model 3s, lead-acid batteries are cheap to make and have been around since the 19th century.

When less expensive is paired with somewhat outdated technology, it’s fair to assume some drawbacks. The most apparent issue is that their electrolytic solution contains sulfuric acid— a highly corrosive substance. And that corrosive substance can ruin your battery terminals, leading to poor charging, slow cranking, low power output and, eventually, the need to replace your battery.

Don’t worry though, it’s not that hard to clean your battery terminals as long as you follow some simple precautions.

clean, battery, corrosion, causes

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What Causes Battery Terminal Corrosion?

At times, the contained sulfuric acid can escape from the battery near the terminals. Sulfuric acid releases hydrogen gas, which reacts with the metal battery terminals, causing corrosion. However, there are several factors that increase the likelihood of corrosion developing. Age, damage, overcharging, and excessive heat can all expedite the corrosion process.

Whenever corrosion forms on the battery terminals, it increases their electric resistance, which reduces the overall conductivity. In turn, low-voltage electronics might malfunction due to the reduced energy supply. Stereos, headlights, and other onboard equipment could suffer from corrosion. In the worst-case scenario, a heavily-corroded battery might fail to engage the engine or high-voltage battery, leaving drivers stranded.

That’s why it’s crucial to monitor the condition of battery terminals, especially if your battery is particularly old or damaged. Luckily, if there is corrosion present, it’s not all that difficult to clean. With adequate materials and safety equipment, getting your battery terminals back to optimal health should take no longer than fifteen minutes.

How To Clean Corroded Battery Terminals

Nitrile gloves and eye protection are essential when cleaning your battery terminals, and having those tools around the house isn’t a bad idea for lots of other tasks. Getty Images

Step 1: Be Safe. When cleaning your car battery terminals, it’s vital to wear some sort of protection to shield your hands and eyes from potential acidic toxins. The chemicals present in the corrosion can burn your skin and eyes, so gloves and eye protection are a must. Rubber or nitrile gloves and safety glasses are usually enough to keep the harmful chemicals off yourself.

Step 2: Disconnect the Battery. Once your gloves and eyewear are on, the most important step is to disconnect the battery connection cables, starting with removing the negative end first. It won’t spark by removing the negative first. Once the positive connector is off, it’s ideal to remove the battery from the car for cleaning, though it can be done inside the vehicle, but it might get a little messy.

Step 3: Get your Tools Ready. Once the battery terminals are ready for cleaning, the actual process can be done in a variety of ways. Many companies sell specialized battery terminal cleaning sprays, though it’s not always necessary. Often, creating a mixture of baking soda and water will suffice. The idea is to create a basic solution that will enable a neutralization reaction between the acidic corrosive material and the alkaline cleaning fluid to occur.

Step 4: Clean. After the solution is ready, it should be applied to the affected terminals and cable connectors. After the reaction takes place, the solution can be agitated on the surface, either with a toothbrush or steel brush. This will break up any remaining instances of surface corrosion. You can repeat this process until the area is clean and clear.

The easiest way to do the actual battery terminal cleaning is with a small brush, like a toothbrush, but there are also spray cleaners you can buy for this task. Getty Images

Cleaning Battery Terminals: The Final Steps

After the surface is free of corrosion, it is ready to be dried with paper towels or a microfiber cloth. Once all moisture is gone, the battery is able to go back to its home. If the battery was particularly discharged, placing it on a tender would be ideal until its state of charge becomes optimal.

With a clean and dry battery, the terminals are ready to meet their connectors. For additional protection, applying battery terminal protector grease will help prevent future corrosion. Battery grease is usually cheap, so it’s usually worth it for added peace of mind. When connecting the terminals, it takes the opposite process as removing them. To reconnect them, make sure to attach the positive end first, then the negative.

In all, cleaning battery terminals is usually a relatively straightforward process. Despite the little time it takes to rejuvenate life into corroded terminals, it can mean the difference of having your car start up and function when needed. With clean terminals, your car battery will be able to function to its maximum extent.

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Frequently Asked Questions (FAQs)

How do 12-volt car batteries work?

For gasoline and diesel-powered vehicles, the engine supplies power to the 12V battery through the alternator. From there, the energy is stored in the battery for the low voltage system and starting the engine. In electric cars, a DC-to-DC inverter is present that draws current from the high-voltage (traction) battery to charge the 12V battery.

Do electric vehicles really have 12-volt batteries?

Yes! As in an internal combustion engine-powered car, EVs need a low-voltage system for accessories because drawing power from the main pack would fry the low-voltage components used for things other than the drive systems.

What are the symptoms of corroded battery terminals?

Difficulty starting your vehicle is the first sign that your battery terminals might be worn, and that includes slow cranking, low power delivery and trouble charging (which might find you repeatedly coming back to a dead battery). There are other problems that can cause these symptoms, but your battery terminals should be the first thing you check. A visual inspection might reveal obvious corrosion, as issues with charging tend to appear with visual cues.

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Unmarked Car Battery Terminals (Beginners Guide With Pictures)

Car batteries, without them, we’re going nowhere; knowing which terminal is which can be a head-scratcher, but five minutes from now, you’ll be an expert.

Car battery terminals will be marked and color-coded. The color red and the plus sign for the positive terminal, and the color black and the minus sign for the negative terminal. The negative terminal connects to the vehicle’s metal chassis.

In this post, I’ll show you clearly which terminal is which, how to fit a battery, and what to do if you connect it back ways. You’ll also learn how to Jumpstart your car.

If your battery is flat and you are locked out of your car, check out the secret fix here.

How Can You Tell Which Terminal Is Which?

The negative terminal is color-coded black and will be connected to the minus side of the battery.

The minus will be stamped into the battery plastic casing; you may need to look closely. The negative terminal may or may not have a plastic cover over the terminal connector.

The negative wiring insulator will be colored black, and the negative terminal attaches directly to the negative side of the battery and to the metal chassis of the car.

If you have ever wondered what the difference is between ground and negative, then this post is for you –“Is ground and negative the same?”

The positive terminal is colored red and will be connected to the plus side of the battery.

The plus sign will be stamped into the plastic battery casing, it may be difficult to spot at first, but it is there.

The positive terminal will likely have a red plastic cover shielding the terminal; it will likely also be marked with a plus sign. The positive wiring insulator will be colored red.

Battery negative identified by a minus sign and black insulator as highlighted above

How To Test A Car Battery?

Battery failure is common, but so too is assuming a flat battery means your battery is faulty. Misdiagnosing a battery can be an expensive mistake.

Checking battery voltage as per the above picture is OK, but a battery that shows a full 12.65 volts could still be faulty. The only way to be sure is to test the battery under load.

The process is simple, but you’ll need a helper and a DVOM (voltmeter). The graphic shows the process, but you’ll need to start the test with a fully charged battery. This test won’t work if the battery is flat.

Step 1 – Charge battery to 12.65 voltsStep 2 – Set the voltmeter to 20v DCStep 3 – Connect the voltmeter as per the graphic aboveStep 4 – Have the helper crank engineStep 5 – A reading on the voltmeter below 9 volts indicates a faulty battery.

If you find your battery has failed, check out the battery blog section, where we cover a ton of battery-buying options.

How To Replace A Car Battery

A car battery will have a fastener on each terminal and a third fastener; the battery hold down, and it secures the battery to the chassis of the car.

Mistakes to avoid:

But before removing any terminals, you should check your driver’s manual; some cars may require calibrating of Windows and steering, and some will need a throttle to relearn, which may require a trip to the shop. I wrote a whole post about recalibrating – Car won’t idle after dead battery.

The more sophisticated the car, the more likely disconnecting the battery will cause issues.

You can avoid all these potential issues by using KAM (Keep Alive Memory); it’s a simple device that keeps power in the car while the battery is removed.

The Schumacher memory saver tool is great, easy to use, pay for itself with just a single use, and is conveniently available on

Step 1: Plug in your KAM device if needed.Step 2: Now we’re ready to change the battery, remove the battery hold-down bolt; it will likely be one bolt at the base of the batteryStep 3: Remove the black, negative, minus terminal firstStep 4: Now remove the red, positive, plus terminalStep 5: Remove the old and fit the new batteryStep 6: Fit the red, positive battery terminalStep 7: Fit the black, negative battery terminalStep 8: Secure the battery with the hold-down bracket

You should note that modern cars employ a battery control module that requires coding to the new battery. A scan tool is required to code the battery to control the module. Your vehicle will still operate without coding the battery, but it will shorten the battery life.

Anyway, it’s all covered in the post I wrote about fitting a car battery, including pictures, and you can check it out here “How hard to fit car battery.”

How To Jumpstart A Car

You’ll need a donor vehicle or a spare battery or alternatively, consider buying a jump pack. The little NOCO boost pack is about the best I’ve seen, and I’ve been a mechanic for over twenty-five years.

It’s small enough to fit in a glove box and powerful enough to start a diesel engine. Anyway, you can check it out here on the Auto electrical tools page.

To jump it with a regular set of jumpers, follow these steps.

Donor car or any fully charged 12-volt battery, the jump-starting procedure is simple. Red positive to red positive booster cable first, then connect the negative black (-) to both battery and chassis or engine ground. A ground is any bare metal on the chassis or engine.

Check the battery and verify both negative and positive markings before connecting terminals.

Step 1:

Move a donor car close enough to connect booster cables.

Step 2:

Put the jumper cables on in sequences 1, 2, 3, and 4.

Step 3:

Start the donor car and leave it idling.

Step 4:

Now start your car and leave the cables attached and your car idling for a few minutes before removing them.

Step 5:

Now with the engine running, remove the jumpers in reverse order 4, 3, 2, and 1. Once running, your car’s alternator will charge the battery back up again; if you wondering how long and want a few tips to help charge it up faster, then check out this post, “How long to charge a battery driving?”

We are assuming; of course, all is OK in alternator land. If you think it might not be, check out this post; we cover alternator testing, and we cover replacing alternators here – “Hard to change alternator?”

Hooked Up Battery Cables Backwards

This is a common enough problem, as is hooking up jumper cables the wrong way. Don’t panic; we’ll figure it out!

Your symptoms could range from:

  • No power at all, anywhere
  • Ignition lights work, but the engine won’t crank
  • Car cranks but won’t start
  • Electrical gremlins since the wrong battery hookup

Hooking the cables up backward will usually blow the main fuse. Fuses are fitted in the under-hood fuse box, interior fuse box, and possibly a trunk fuse box.

First, locate your handbook or Google where your fuse boxes are, and you’ll also need to know the individual fuse locations.

If you have no power at all, anywhere, first verify that your battery is OK. You can check it with a voltmeter (12.65v is full) or using booster cables from a fully charged 12v battery; use the jump-starting guide above.

You can find a simple handheld battery tester listed here on the “Auto electrical repair tools page.”

If the battery checks out, then go ahead and check the fuses.

A blown fuse will have a broken element visible through the plastic body. A tweezers tool fitted to the inside fuse box cover will help with removal. Your fuses may not look identical to those shown here, but you get the idea.

Look for the following fuses; you won’t have all of these but check whichever ones you’ve got.

  • Main fuse
  • Battery monitoring fuse
  • ECU/ECM/PCM fuse
  • CEM fuse
  • Instrument panel fuse
  • Car fuse bank

If your ignition lights work, but the engine won’t crank, check the following fuses:

  • Main fuse
  • Anti-theft fuse
  • Immobilizer fuse
  • ECU/ECM/PCM fuse
  • Starter motor relay/fuse
  • Ignition fuse

If none of this helped, check out this post; it covers all the fixes for mixing up the terminals – “Battery sparked now won’t start.”

Check out this post also; it covers fault finding a no crank “Car won’t start clicking noise”

Fuse types and color chart.

If your car cranks but won’t start, check the following fuses:

  • Main fuse
  • Anti-theft fuse
  • Immobilizer fuse
  • Ecu/Ecm/Pcm fuse
  • Ignition coil fuse
  • Fuel pump fuse
  • Fuel injector fuse

The battery can drain for a ton of reasons; as you know, battery failure is the most common cause, but a short in the wiring system can drain your battery too. A persistent unexplained drain points to a short so long as your alternator and battery tested OK. I cover testing both battery and alternator here in this post, “Car battery drain”

If you think you have a wiring short you can check out my beginner’s guide to finding a short right here.

Having a workshop manual for your vehicle is always a good plan; they only cost a few dollars but will save you a packet. A good manual will cover your vehicle in detail, including repair and replacement procedures, electrical wiring diagrams, system overview, troubleshooting section, fastener torque specs, etc., all mission-critical info.

You may find the following links helpful:

Related Questions

Which terminal is ground on a car battery? The ground terminal is the black minus terminal on the battery, also known as the negative or ground terminal. It connects the vehicle chassis to the minus side of the battery.

John Cunningham is an Automotive Technician and writer on He’s been a mechanic for over twenty-five years and has worked for GM, Volvo, Volkswagen, Land Rover, and Jaguar dealerships.

John uses his know-how and experience to write fluff-free articles that help fellow gearheads with all aspects of vehicle ownership, including maintenance, repair, and troubleshooting.

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