Battery Sulfation

Battery Sulfation refers to the buildup of lead Sulfate crystals on the plates of lead acid batteries. Actually, it is one of the major causes of early failures of sealed or wet cell batteries (along with vibration and damaged charging plates).

What Causes a Sulfated Battery?

Sulfation is not a strange phenomenon. Lead acid batteries often develop Sulfate during their years of use. The sulphuric acid electrolyte attacks plates forming lead Sulfate as the battery self-discharges. It doesn’t matter if batteries are undercharged, overcharged, or discharged they will quickly develop Sulfate. Some of the notable causes include:

  • Battery lying idle for several days between charges
  • Battery is stored without any type of energy input
  • ​Low electrolyte levels which expose plates to air
  • ​Undercharging battery
  • Incorrect charging levels

Even when a lead acid battery is stored while fully charged the Sulfate will still develop unless a desulfating charger is used. 

Storing or using batteries in temperatures over 75°F increases the rate of self-discharge as well as Sulfation. In fact for every 10°F increase in room temperature, there is a corresponding increase in the rate of Sulfation.

Levels of Battery Sulfation

Sulfation manifests in three levels; spongy, barrier, and crystallized. Each stage reflects the state of the Sulfate and internal level of impedance.

Let’s look at what happens at each level.

  • Spongy: lead Sulfate assumes a spongy form. Water and lead dioxide are produced. In this stage, the battery has a low impedance usually less than 6 mΩ. The spongy Sulfate can be converted back to lead when the battery is charged.
  • Barrier: small crystals coalesce around the plates as a result of covalent bonds. The battery develops a higher internal impedance and may not be able to start a car.
  • Crystalized: Eventually large crystals form as a result of the stronger bonds around the lead plates. At this stage, the impedance is very high and there’s little surface area left for chemical reactions to take place.

What are the Effects of Sulfation?

Sulfation almost always has a negative impact on the shelf life and the functional efficiency of lead batteries. The impact becomes pronounced as the years go by.

Battery Sulfation

When Sulfation occurs, it leads to:

  • Prolonged charging times
  • Loss of cranking power
  • Shorter battery shelf-life
  • ​Extreme heat buildup
  • Reduced running times (between charges)

Sulfation also causes active materials on lead plates to disintegrate and fall to the bottom of cells. As materials build up on the bottom, they eventually cause a short circuit.

Worthy of mentioning is the fact that Sulfation crystals also form an insulating layer on plates, lowering the battery’s ability to deliver high current.

The below video helps explain sulfation and its effect on lead-acid batteries:​

Reversing Sulfation in Lead Batteries

Sulfation can be reversed safely using desulfating battery chargers or by slow trickle charging. Proper charging and recharging a battery also helps to reduce the formation of Sulfates.

While some chargers can remove Sulfates, only pulse-type chargers with high frequency electronic pulses can effectively dissolve hardened Sulfates. Where Sulfation is severe the batteries may not be recoverable.


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