Understanding Lead Acid Battery Sulfation and How to Avoid It

What is Lead Acid Battery Sulfation?

Battery sulfation is the buildup of lead sulfate crystals on the plates of a lead-acid battery. In a healthy battery, the lead plates (positive and negative) are immersed in a mixture of sulfuric acid and water. During normal battery operation, lead sulfate forms on the plates as part of the chemical reaction that generates electricity. However, this lead sulfate is usually converted back to lead, lead oxide, and sulfuric acid during the charging process.

Sulfation becomes problematic when the battery isn’t recharged for long periods. The lead sulfate crystals grow and harden, making it difficult or impossible to convert back into active materials during charging. This buildup can reduce the battery’s capacity to hold a charge, increase internal resistance, and eventually lead to battery failure.

Lead Acid Battery Sulfation Is One Of The Leading Causes of Battery Failure

Several factors can contribute to the formation of harmful lead sulfate crystals on battery plates. The most common causes include:

1) Undercharging— One of the primary causes of sulfation is undercharging, which occurs when a battery is not fully charged after each use. This is common when drivers use their vehicles predominantly for short trips. That causes the battery to expend more power than is put back in during the short trip. Over time and with prolonged periods of discharge, the lead sulfate formation eventually causes the battery to fail and not accept and hold a charge.
2) Infrequent Use or Long Periods of Inactivity— All batteries, including lead acid batteries, self-discharge over time, with a higher rate of discharge in hot weather. In the case of car batteries, the discharge is accelerated by the fact that the vehicle’s computer systems draw a small amount of power 24/7 to keep the computers awake. When left unused for long periods, as we saw during the pandemic, the self-discharge and current draw cause lead acid battery sulfation that can permanently damage the battery.
3)  Overdischarging— Overdischarging usually doesn’t occur from the vehicle’s charging system. It’s more common when an owner connects an older, non-computerized battery charger, leaving it in place for longer than needed to top off the battery. Older non-computerized battery chargers can charge at a voltage at high as 17-18 volts which overheats the battery, causing sulfation and plate damage.
4) High Temperatures— Excessive heat can accelerate the sulfation process by increasing the rate of chemical reactions within the battery. High temperatures cause the electrolyte to evaporate more quickly, leading to higher concentrations of sulfuric acid and a greater likelihood of lead sulfate formation. Batteries exposed to high temperatures for prolonged periods are more susceptible to sulfation and other forms of damage.
5) Using Incompatible or Poor-Quality Chargers— Using a charger that is not suited for your battery type or one that delivers an incorrect charging voltage can contribute to sulfation. For example, a charger that undercharges the battery or does not have a proper float charge setting can leave the battery in a partially charged state, promoting sulfation.

When a lead-acid battery sits in a discharged state, whether due to leaving lights or leaving your vehicle unused for long periods of time, the lead plates develop a coating of lead sulfate. The longer the battery sits unused in this state, the more the plates accumulate lead sulfate. And, the deeper the discharge, the worse the sulfation becomes. If the battery is left in this state for long periods, the lead sulfate begins to crystallize. The non-conductive sulfate crystals clog the porous plates to the point where the battery will no longer accept or hold a charge.

This sulfation process happens in all lead-acid batteries: flooded lead acid (SLI), enhanced flooded battery (EFB), absorbed glass mat (AGM), or gell-cell batteries.

Preventing and Reversing Battery Sulfation

Preventing battery sulfation is more effective than reversing it once it has occurred. Here are some strategies to help prevent and manage sulfation:

1. Drive the Vehicle At Highway Speeds or Regularly Charge the Battery

If you take short trips in stop-and-go traffic during the week and use lots of electrical accessories like AC, Heat, Heated Seats, Rear Defogger, get it out on the highway for at least 20 minutes every weekend. That’ll allow the charging system to run at a high enough speed to recharge the battery. If you can’t do that, at least buy a battery maintainer and place it on the charger overnight once a week. that  Regular charging prevents the buildup of lead sulfate crystals by fully converting them back into active materials.

2. Avoid Long Periods of Inactivity

If a battery is going to be inactive for an extended period, consider using a battery maintainer to keep it in a fully charged state. This will prevent the formation of lead sulfate crystals during periods of inactivity.

3. Store Batteries Properly

Store your unused starting or marine batteries in a cool, dry place away from direct sunlight and heat sources. Keeping the battery at a moderate temperature will slow down the chemical reactions that lead to sulfation.

Lead Acid Battery Sulfation Symptoms

1) Reduced Battery Capacity— As sulfation progresses, the battery’s ability to hold a charge diminishes. This results in a reduced capacity, meaning the battery cannot store as much energy as it could when new. That results in shorter cranking times, and lower reserve capacity.
2) Increased Internal Resistance— The buildup of lead sulfate crystals on the battery plates increases the internal resistance of the battery. Higher internal resistance reduces the efficiency of the battery, leading to slower charging, reduced power output, and increased heat generation during use. Increased internal resistance reduces the amount of power available to start your engine.
3) Difficulty in Charging— A sulfated battery can be difficult to charge. The hardened lead sulfate crystals resist the chemical reaction needed to convert them back into active materials, resulting in slow or incomplete charging. In severe cases, the battery may not charge at all.
4) Shortened Battery Life— Sulfation significantly shortens the lifespan of a lead-acid battery. As the sulfate buildup progresses, the battery’s performance continues to degrade until it eventually fails. This often leads to premature replacement of the battery, increasing costs and inconvenience.

The right hand cell of this 6-volt battery shows severe battery sulfation

The chemistry behind battery sulfation

Batteries produce power through a chemical reaction between the lead plates and the electrolyte (battery acid).

Car battery acid is a diluted solution of sulfuric acid H2SO4. In simple terms, the battery acid provides the sulfate, hydrogen, and oxygen needed to interact with the plates to produce power.

When a car battery is discharged through use or from self-discharge from non-use, the sulfuric acid in the electrolyte combines with the lead (Pb) to form a coating of lead sulfate (PbSO4). The sulfate crystals reduce the plate’s active/reactive surface area, which, in turn, reduces the battery’s ability to produce power.

Worse yet, the sulfate crystals act as an electrical insulator, increasing the battery’s internal resistance. When fully sulfated, the battery acid has given up most of its sulfate and hydrogen. At that point, all that’s left is water H2O. That’s why discharged car batteries freeze in cold weather.

If caught early enough, recharging can partially reverse the process

During recharging the alternator pushes the sulfate and hydrogen off the plates and forces it back into solution, turns the H2O back into H2SO4. However, that only occurs if the sulfate crystals are soft.

However, if the sulfation is ignored and left in place for weeks or months, large portions of the lead plate surface become permanently unavailable. That dramatically reduces the battery’s ability to produce starting power. It may fail to produce enough power to operate the starter in warm weather and may even fail to provide enough power to light the lights in cold weather.

The longer a battery sits in a discharged state, the more likely the battery is permanently damaged. As a battery sits in the discharged state, the sulfate crystals grow in size and harden. After a certain period of time, they’re impossible to remove, even with recharging. At that point, the battery must be replaced.

Can you desulfate a battery?

If the sulfation is the reversible soft crystal type, you can reverse it by recharging. But the recharging process is somewhat tricky. For example, a battery charger that’s equipped with a six-phase battery reconditioning routine may start by recharging process at a low voltage, around 4 volts and 7 amps. That’s called the energizing phase. Why low voltage? Because a sulfated battery has developed high internal resistance. If you hit it with high voltage right off the bat, that high resistance will create HIGH HEAT, and that heat will warp the plates and short out the battery.

Next, the charger boosts the charging current to around 13.5 amps while slowly ramping up the voltage to a peak of around 14.5 in phase 3. In the third or absorption phase, it maintains constant voltage while ramping down the amps. The 4th phase drops the voltage slightly and the amperage a bit further. In the 5th or resting phase, it drops current flow to 0 while maintaining around 12.5 volts. The 6th phase exercises the battery by pulling a load on the battery until it reaches the final restoration phase where it raises amperage and voltage one last time. The key to reconditioning a battery after sulfation is to prevent overcharging and overheating.

If the sulfation crystals have hardened, there’s no way to reverse the process and the battery must be replaced and recycled. Although, one company claims it can reverse sulfation.

©, 2020 Rick Muscoplat