What Is That White Powder On My Car Battery Terminals?

Leaving white power on a battery is the sign of corrosion.

When I opened the hood of my car and saw white scum on top of my battery, my first thought was, what is that white powder in my car battery? For an ignoramus like me, the sight of that whitish/bluish powder coating the car battery terminal caps and the area around them is quite alarming.

But, I took pains to find out what it is, what causes it and how to remove it and even how to minimize the unsightly gunk since it cannot be totally avoided. In this article, I would like to share with you what I found out.

What is that whitish (sometimes blueish/greenish) powdery substance in a car battery? The whitish/bluish powdery stuff in a car battery, particularly on the battery terminals and the area that surround them, is called corrosion. It is something that is commonly found on lead-acid batteries, the battery that is being used for most cars.

What Causes Corrosion?

Corrosion is the result of the reaction between the sulfate in your battery and the lead substance in the terminal posts. It develops mainly on the grid, It is the byproduct of a chemical reaction that causes the lead plates to soften and shed. This is an unavoidable occurrence since the plates in a lead-acid medium are continuously reactive. The shedding of lead is a reality that cannot be avoided, but can be minimized.

When the corrosion coats the terminal posts or is on top of the cell of your battery, it is corrosion caused by the chemical reaction between the battery terminals, connectors, and lugs. This usually occurs because of a defective seal, but can also be brought about by overcharging or when the battery is quite old.

When it is the terminals that are corroded, it is usually due to the release of hydrogen gas from the acid in the electrolyte. When the corrosion is in or around the positive terminal, it is generally the result of electrolysis because of the incompatible metal alloys used in producing the cable connectors and battery terminals.

A white powdery substance is normally, zinc sulfate or lead crystals. A blue and white powdery stuff comes from the corrosion of copper connectors. Aluminum connectors get corroded with aluminum sulfate.

Another possible cause of corrosion will be thermal expansion due to over-filling the electrolyte with water. A thermal expansion could push the acid and water mixture out of the battery vents located on top of the battery. This spilled electrolyte could react with the metals in the battery connector that will generate corrosion.

There is also a possibility for the electrolyte to seep out of the seals where the terminals go through the plastic case and react with the lead and other metals.

Acid fumes that escape out of the vent caps are usually brought about by lack of ventilation in the battery box or by overcharging. An acid fume build-up can also cause a chemical reaction when it comes in contact with the exposed metals of the battery.

Extended or drawn-out overcharging is one more cause of corrosion, especially to sealed lead-acid batteries that need to operate on the suggested float chart such as an Absorbent Glass Mat (AGM) BATTERY. Flooded or wet lead-acid batteries are more adaptable to overcharging.


When talking about corrosion, you can’t avoid discussing sulfation also. You see, if the white powdery gunk that you see on your battery is in the negative terminal, this is not just simple corrosion. This is already the result of sulfation, a more serious problem than corrosion.

Sulfation is the accumulation of lead sulfate crystals. This is usually due to a lead-acid battery not being properly charged or not charged enough and is the usual cause of its premature failure.

When you frequently drive your car only for short distances and your car is electronic accessory-heavy, your alternator may not be operating long enough to give your battery a proper charge.

While the battery is being used, there are tiny sulfate crystals that are being formed. There is nothing to worry about these tiny crystals since these are normal and will not harm your battery.

But, if your battery is repeatedly being deprived of a proper charge for an extended period of time, these tiny blobby crystals settle into the negative plates. Then, they develop into sizable crystals that lessen the active material of the battery which accounts for the battery’s performance.

Sulfation is the number one cause of the premature death of a car battery.

Effect Of Corrosion In The Performance Of A Car Battery

Ordinary corrosion or a small amount of corrosion will not affect the performance of your battery. However, if the build-up accumulates, it can affect the delivery of power from the battery to the engine. And, you might find it harder to start the car or it could even totally prevent the car from starting.

The electric charge stored in the battery has to be delivered to the engine in order for the car to start. If the build-up of corrosion on the terminals is excessive, transferring of current from the terminals to the engine could be curtailed or diminished to the point where your car will refuse to start. In such a case, you will need to jump-start your battery so that you can keep going.

Problems other than the engine refusing to start could also manifest. This includes car accessories such as the cabin light and the radio, among others, to malfunction or fail to switch on because of lack of power.

If the condition is not corrected and the build-up continues, even the onboard computer may stop operating. Your car’s onboard computer gathers vital information coming from the car sensors to keep it running, warns you of potential problems, and keep your car and you safe. Not doing anything with the build-up of corrosion could put you at risk.

Also, when the corrosion is on the negative plates, this is no simple corrosion but a more serious issue called sulfation. It could cause your car battery to die prematurely.

What To Do To Minimize Corrosion

Although there is no way to prevent corrosion since it is a natural phenomenon on a lead-acid battery, especially the wet or flooded kind, there are ways to minimize it.

Here are ways of minimizing corrosion:

1. Once you see signs of corrosion on your battery, hasten to remove it. In getting rid of the corrosion, you must make sure that you are adequately protected since you are dealing with acid here. Wear protective gloves and goggles, old long-sleeved shirt, and footwear with covered toes.

Your cleaning paraphernalia includes a stiff wire brush, rags and a mixture of baking soda and water.

Disconnect the cable from the posts so that you can clean the posts, cables and the top surface of the battery thoroughly. Apply the baking soda and water solution and vigorously brush the corrosion from the battery. Finish off by wiping dry the entire area with the rag.

Once you’re through cleaning, reconnect the cables and fasten them tightly. Then, apply grease on the terminals. The purpose of the grease is to prevent corrosion from occurring again. The grease prevents the conducting surfaces from reacting with the moisture and surrounding air, thus preventing corrosion.

Greasing clean terminals regularly is advisable since, after some time, the grease will disintegrate and corrosion could set in again.

2. Limit the depth of discharge. DoD or depth of discharge appertains to the amount of energy cycled into the battery and out of it during every cycle. Depth of discharge differs from cycle to cycle. But, in general, the maximum DoD for lead acid batteries is at 50% or even lower than the battery’s total capacity.

3. Operate at a moderate temperature. Batteries can operate at a wide range of temperature. But high heat and extreme cold lessen the battery’s ability to accept a charge so that charging under extreme conditions could result in undercharging.

Use a charger with varying float voltages and calibrate the charge voltage to the ambient temperature. Reduce the float charge when the prevailing temperature hits 85°F or 29°C and raise it up when the temperature is colder. This will minimize corrosion.

4. Avoid or control overcharging. When the battery is being undercharged or overcharged it releases excessive hydrogen gas which reacts with the battery’s metal parts causing the build-up of corrosion.


Now, when I see that white powder in my car battery I no longer get inordinately alarmed. I tell myself it’s only corrosion which is a normal phenomenon in lead-acid batteries. Having such knowledge is such a relief, especially since I have also learned how to deal with it.

My goal now is to try to lessen or slow down the build-up of corrosion, and following the suggestions which I have itemized here, is not at all difficult to do. I guess, the key to having a healthy battery with a minimum of corrosion is still the proper care and maintenance of my battery.