This article is all about sulfated batteries.

Battery sulfation is a big problem in the motive power world.

So, we’re going to give you the tips you need for battery sulfation prevention and restoration.

You’ll learn:

  • What sulfation is
  • What causes sulfation
  • How to prevent sulfation
  • How to revive a sulfated battery
  • And lots more!

Let’s dive in!

What Is a Sulfated Battery?

To understand sulfation, we first have to understand how lead-acid batteries work.

Invented in 1860, lead-acid batteries are the most common and widely used type of battery.

Lead-acid batteries are composed of:

  • Cells
  • Lead plates
  • Electrolyte (sulphuric acid and water)

Each cell contains alternating lead and lead oxide plates and separators immersed in the electrolyte.

An illustration of the components of a flooded lead-acid battery
Sulfation occurs when electrolytes combine with the lead electrodes

As electrical current flows through the battery, the electrolyte reacts with the lead plates.

When this happens, sulfuric acid in the electrolyte combines with the lead material.

And that turns both plates into lead sulfate.

This is precisely what sulfation is.

Is a Sulfated Battery Bad?

Yes, it is.

In fact, sulfation accounts for many early battery failures.


Because as the battery discharges, the lead sulfate builds up more and more on the plates.

This in turn reduces the surface area of the plates.

As a result, the battery has less active material from which to produce power.

This process can lead to:

Loss of cranking/starting power

Longer charge times

Lower run times between charge times

Shortened battery lifespan

Premature or complete failure

Battery boilovers

Increased heat build-up in the battery

What Are the Different Types of Sulfation?

There are two types of battery sulfation:

  1. Reversible sulfation
  2. Permanent sulfation

These names imply exactly what each means for the battery.

Reversible sulfation can be reversed.

But you’d need to recognize sulfation early enough for it to be reversed.

If left to accumulate for a long time, it’s highly unlikely you’ll be able to reverse sulfation.

If that happens, the battery will become permanently sulfated.

A sulfated forklift battery
This forklift battery is permanently sulfated. Note the overflow of sulfation on the sides

Also called hard sulfation, permanent sulfation occurs when a battery has been in a low state of charge for a long time, such as weeks or months.

Now, despite the term, permanent sulfation can sometimes be salvaged.

But, it’s highly unlikely.

What Are the Causes of Battery Sulfation?

Sulfation is normal in all batteries.

In fact, it’s a key part of the electrochemical process that generates power.

It’s also only temporary.

That’s because the process is reversed when the battery is recharged.

A forklift battery on charge
Sulfation is a normal part of lead-acid batteries and is reversed during charging

However, the problem is when the sulfation builds up excessively.

And that can happen if the battery is:



Not in use for a prolonged time (charged or discharged) such as weeks or months

Stored without a full charge

Additionally, you need to be mindful of the temperature that you’re storing or using batteries in.

That’s because temperatures above 75°F will speed up sulfation.

In fact, a battery’s discharge rate doubles, as does sulfation, with every 10°F rise above 75°F.

How to Prevent Battery Sulfation

Now that you know what causes sulfation, it’s easier to understand how to prevent it.

Consider the following suggestions:

Allow the battery to charge fully regularly. And don’t allow it to drop below 12.4 volts

Ensure proper battery storage. Don’t leave batteries discharged and unused for extended periods

Apply a top-up maintenance charge periodically if the battery is in storage

Keep the battery’s temperature below 75°F (24°C)

Perform regular battery maintenance. The less maintenance you do on your battery, the faster lead sulfate crystals will build upon the battery plates

These precautions are key.

Because once excessive sulfation has formed, it may not be possible to reverse it.

How to Tell If Your Battery Is Sulfated

If your battery is a victim of sulfation, you’ll notice signs of decreasing battery efficiency.

But, battery efficiency comes from different angles.

So, if your battery is sulfated, you’ll notice some of the following sulfated battery symptoms:

The battery will not charge very well. Or, it simply refuses to charge at all. This is the most common sign of sulfation

The battery will not hold a charge and goes dead long before expected

Your electronic accessories are not getting enough power or amperage. Look for things like dim headlights, slow startup, weak air conditioning, etc.

How to Check if Your Battery is Reversibly or Permanently Sulfated

To know whether you can reverse the sulfation or not, you can check the battery’s voltage discharge curve.

A downward curve on a graph
A temporarily sulfated battery should hold a stable voltage profile. A permanently sulfated battery will not

Here’s what to look for:

Make sure the battery is fully charged. Can the battery hold a stable voltage profile on discharge? If it can, it may be reversibly sulfated

Does the voltage drop rapidly with load? Then it’s highly likely that it’s permanently sulfated

What Does a Sulfated Battery Look Like?

Visually, you may not easily notice any difference in battery appearance between a normal and sulfated battery.

But, you can still check a few things.

First, look for a build-up of a white powdery substance on the outside of the battery.

Sulfation on the terminal of a battery
Note the build up on this battery terminal - a sign that it’s sulfated

While not a conclusive indication of sulfation, it’s a strong sign.

You can also tell from looking inside of the cells.

Just be careful, because this requires opening up your battery.

And that can expose you to corrosive sulphuric acid and hydrogen fumes.

So it is recommended to do this in a covered, well-ventilated area.

Here are the steps:

  1. Carefully remove the caps

  2. Look inside each hole to view the battery’s plates, separators, and electrolyte levels

A typical sulfated battery will have grayed and grimy plates.

A damaged lead-acid battery with plates exposed
The plates in this damaged battery are gray and grimy, a likely consequence of sulfation

It may even be hard to distinguish them from each other.

On the other hand, a healthy battery will have clean silver-lead plates.

A brand new lead-acid battery with the cover off
How a non-sulfated battery’s plates should look - silver and shiny

These should be clearly distinguishable from the black separators.

Battery Sulfation Testing

If you can’t tell the difference, your next best option is to conduct a battery sulfation test.

You can do this by testing the battery’s standing voltage using a multimeter.

A red multimeter
You can use a multimeter to check for battery sulfation

Any voltage less than 12.6 volts for an AGM battery indicates that your battery is undercharged.

And that's possibly the result of sulfation.

How to Properly Recover and Recondition a Sulfated Battery

Remember, you can usually only recover a sulfated battery if it's reversibly sulfated.

So, how do you do it?

There are two methods to bring a reversible sulfated battery back to health:

  1. Overcharge the battery with high bursts of voltage
  2. Pulse charge with high-frequency energy

We’ll cover each method in more detail below.

Method 1: Overcharging the Battery With High Bursts of Voltage

The first question you might wonder is: “Can a sulfated battery be charged?”

The answer is yes.

But you’d have to overcharge it if you want to reverse the sulfation.

You can do this by applying high bursts of voltage to an already fully charged battery.

Illustration of a jolt of electricity
The first method to remove sulfation is using high bursts of voltage

This is done using a battery desulfator, which puts out a regulated current of about 200mA.

Generally, the battery terminal voltage can be allowed to rise to between 2.50 and 2.6 volts per cell (15V and 16V on a 12V monoblock) for around 24 hours.

And that current will help dissolve the lead sulfate crystals.

Also, the overcharge will increase the battery’s temperature to 122–140°F (50–60°C).

And that further helps dissolve the crystals.

Method 2: Pulse Charging With High-Frequency Energy

In this method, you can use a desulfating battery charger to reverse the damage.

Doing so involves using high-frequency electronic pulses to dissolve the crystals.

That’s in contrast to method 1, which uses high voltage.

Here’s how it works...

The pulse charged is followed by a rest period.

Then, sometimes a very short discharging pulse occurs to refresh the discharge.

An illustration of high-frequency waves
The second (controversial) method of removing sulfation is using high-frequency pulses

Using high-frequency pulses can help reverse or delay sulfation and prolong the battery’s life.

But this method is a little controversial.


Anti-sulfation devices (such as a desulfating battery charger) can apply pulses to battery terminals to prevent and reverse battery sulfation.

But they won’t reverse the damage completely.

So, these devices aren’t always recommended.


There you have it: Our tips for preventing and restoring a sulfated battery.

Now, we’d like to hear from you.

Knowing what you now know, could you fix a sulfated battery?

Let us know in the comments section!