What does “Sul” mean on a battery charger?

What does “Sul” mean on a battery charger? Batteries, be they of vehicles or other categories, are the main DC power source in most electric systems.

While they can provide enough energy for components to turn on and work efficiently, they need rejuvenation occasionally to prevent sulfation

You may have heard of sulfation affecting the batteries but do not know the science behind it.

This article will examine the phenomenon deeply while discussing some popular prevention methods.

What is Sul/Sulfation?

Lead-acid batteries have plates made of lead suspended in an H2SO4 solution.

The lead and the sulphuric acid produce lead sulfate, forming a layer over lead plates.

As time passes, this byproduct stiffens on the plates, turning into crystal form and are insoluble.

Due to their accumulation, the capacity of lead plates to store charges slowly becomes lower. 

Separating the sulphuric acid and the lead is not a solution here since you need a metal and an electrolyte to generate the charges.

Hence, you need other methods to recondition the plates without replacing them.

Why sulfation occurs?

Before understanding the reason behind sulfation, we have to look into the working of car batteries

Types of a car battery

There are three lead batteries, AGM, Flooded(wet), and Gel.

Every lead-acid battery has 6 cells providing 2.13V. When you charge it fully, its total voltage is around 12.72V.

These cells have one +ive with lead dioxide plating and one -ive plate with sponge lead as active material.

Here, the active material is the material that chemically reacts with the battery’s acid to produce charges. 

Most auto vehicles use flooded (wet) batteries filled with free-flowing liquid and electrolytes. It is usually a mix of water and H2SO4.

Discharging a lead-acid battery

Discharging a battery means connecting to some components for power when using it. Also, the batteries can self-discharge when you aren’t using them. 

When the H2SO4 reacts with the +ive lead oxide plate, it creates hydrogen, and oxygen ions, forming the water.

Moreover, it also leads to creating the PbSO4 on the surface of the +ive plate.

On the -ive side, the H2SO4 reacts, forming lead sulfate and discharging a free electron.

When the battery charging is full, there is an excess of free electrons over the -ive plates.

On the other hand, the +ive plate has no charge, causing a potential difference between the two sides, and hence, the voltage is 12.7V at full charging. 

Checking the voltage of a vehicle battery

Checking the voltage of a vehicle battery

How does the battery power components?

When a device is connected, electrons transfer from the -ive side to the + side in the battery, thus powering the device.

The current flow is this sort of movement, where the electrons move and produce electricity.

This way, the battery transfers its electric energy to the device you connect it to.

Discharging a battery creates sulfation. It is because lead sulfate accumulates on the plates, and the acid dilutes.

The reasons for this are :

  • There’s less acid (as the sulfate reacts with the lead to make lead sulfate, i.e., PbSO4.
  • Water is produced during this chemical reaction.

Hence, the lead sulfate accumulates on the plates as a byproduct of this chemical reaction.

Charging a battery

Charging is the opposite process.

The charger sends electrons to the -ive plates of the battery, which move to the +ive plates via the electrolyte.

This chemical change results in a difference in energy between the plates, i.e., a Voltage.

This way, the battery becomes a store of energy ready to release.

To charge the battery, you must set a higher voltage across it than its existing voltage.

However, a too-high voltage will cause gassing of the acid.

During this process, the residue breaks down and separates into lead, and the sulfate returns to the sulfuric acid in the solution.

This way, the acid becomes concentrated. 

Do good charging particles prevent sulfation?

No, not completely.

However, you will have less sulfation if the charging particles are good. Ideally, a lead-acid battery should have lead sulfate gathering over the plates when the energy discharges, and as you charge it, the lead sulfate will dissolve in the electrolyte.

However, in reality, the process doesn’t work like that.

Most people will not get their battery fully charged frequently at an appropriate voltage and stage.  

Perfect charging cycles are impossible.

Even if you managed it, you’d still have sulfation, and sometimes it can’t break down just by the ordinary charging process.

What causes Sulfation to grow?

Here are the main causes that can let sulfation grow.

Removing battery corrosion

Removing battery corrosion

Not using the battery

If you don’t use the battery long, sulfation will occur on the plates.

The longer you leave the battery partially discharged, the higher will be the accumulation rate.

Charging a battery makes the lead sulfate return to its original state.

So, if you don’t charge it for a long time, the lead sulfate stiffens and turns into larger clumps. 

 Undercharging a battery

Sulfation is brought on by more than only discharge.

It can worsen if the battery doesn’t receive a higher charging voltage.

The battery won’t receive enough power from the charge voltage if it is lower than needed to dissolve the particles on the plates and restore them to the electrolyte.

Therefore, the charge voltage should always be greater than the battery’s current voltage.

Effects of sulfation

Due to sulfation, batteries do not complete their time and die faster.

Sulfation blocks the chemical energy in car batteries from releasing, so you may junk them to their full potential. 

It is because lead plates have a layer of lead sulfate crystals all over them, leading it to hide all the metal underneath that is responsible for producing charges. Hence, the battery stops functioning.

How does desulfation work?

You can recondition the battery in two ways.

Use a conditioner or desulfation charger (a battery charger with desulfation mode)

A desulfation charger combat sulfation by giving the battery a full charge, and under its desulfation mode, it can remove the lead sulfate crystals. 

Use a desulfator

A desulfator permanently attached to the battery does not allow sulfation in the first place, even when discharged.

High-frequency pulses remove sulfates every moment you drive, arguably the most effective battery restoration practice.

It’s always better to preemptively act on something than to react to it after it happens.

Both of these methods have the same working conditions i.e. use of clamps and high-frequency pulse is required.

High voltages can remove the lead sulfate particles from the plates.

However, constant exposure to such high voltage can raise the battery temperature and be dangerous in the long run.

So, these pulses are short blasts of high frequency; thus, they do not hold much danger to the system.

As a result, you will get clean plates without any sulfation.

The residue lead sulfate will again dissolve into the electrolyte, making it part of the battery’s charge process. 

Effects of Desulfating a Battery 

Changing a Car battery

Changing a Car battery

Desulfation decreases the battery’s internal resistance, enabling it to hold more charges.

You may have noticed that sulfation reduces the battery’s capacity to hold the current, delivering less power, especially in cold winters.

Due to sulfation, the lights dim, and the sound system may become lower in volume. 

After you are done with battery reconditioning, you will see that the battery is charging properly and isn’t dying frequently.

Starting the vehicles is becoming easier, and the components have sharper lights and sound.

Additionally, it has added life to your battery, often several years before it can completely get useless.  


Sulfation is the most common culprit behind dying batteries.

Since batteries are expensive, changing them frequently can cost you a lot of resources.

In such cases, desulfation will help you clean the battery plates while reconditioning them for further use.