Rick's Free Auto Repair Advice

What causes battery sulfation?

Battery sulfation definition and prevention

What causes car battery sulfation?

• Deep discharge—like leaving your lights on overnight

• Self-discharge—all lead acid batteries self-discharge about 1-2% per day, depending on the storage temperature (faster in higher heat).

• Long periods of discharge— The longer you leave a battery in a discharged state, the more the sulfation process becomes a problem.

• Faulty charging system—If the alternator isn’t working in your car, you’ll draw more power from the battery than you’re returning. That will cause sulfation.

How does a battery sulfation happen?

This is a simplified explanation. 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 pates and produce power. When a car battery is discharged, the sulfate that was in the acid, is now attached to the surface of the plates. The sulfate crystals reduce the plate’s 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 (keep this in mind when we cover recharging). At this point, the battery acid has given up most of its supply of sulfate and hydrogen. All that’s left is water H2O. That’s why discharged car batteries freeze in cold weather.

Recharging reverses the sulfation process — to a point

When the alternator is operating properly, it literally pushes the sulfate and hydrogen off the plates and forcing it back into solution, which turns the H2O back into H2SO4. But it doesn’t always work that way as you’ll see below.

Two types of battery sulfation

There are two kinds of car battery sulfation; the reversible (soft crystal) type and the permanent (hard crystal) type. If reversible sulfation is caught early, it can be eliminated with recharging at the proper rate. But if the sulfation is ignored and left in place for weeks or months, large portions of the lead plate surface area will 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?

You can desulfate a battery if the sulfation is the reversible soft crystal type. 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 develop 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 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 drop 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.

battery sulfation

Battery reconditioning protocol — Clore Automotive

What about those “miracle” battery desulfation chargers?

Some companies promote a battery desulfating charger that works by introducing a range of high frequency pulses at low voltage. The pulses supposedly break up and dissolve the sulfate crystals in a short time period. Do those device work? Partially. They can reduce soft crystal sulfation, But I’m not convinced they reduce large hard sulfate crystals. s

Here’s a comment from BatteryUniversity.com on the effectiveness of pulse desulfation:

“Applying random pulses or blindly inducing an overcharge can harm the battery by promoting grid corrosion. There are no simple methods to measure sulfation, nor are commercial chargers available that apply a calculated overcharge to dissolve the crystals. As with medicine, the most effective remedy is to apply a corrective service for the time needed and not longer.

While anti-sulfation devices can reverse the condition, some battery manufacturers do not recommend the treatment as it tends to create soft shorts that may increase self-discharge. Furthermore, the pulses contain ripple voltage that causes some heating of the battery. Battery manufacturers specify the allowable ripple when charging lead acid batteries.”

How to prevent car battery sulfation?

• Don’t just start your car in cold weather and let it idle. The alternator doesn’t provide much power at idle speeds. DRIVE IT on the highway to get the RPMs up.

• Maintain your charging system. Make sure the alternator drive belt and the belt tensioner are in good condition to prevent slipping. See this post on checking your serpentine belt and belt tensioner.

• Don’t let a car sit unused for long periods. Remember, car batteries self-discharge at the rate of 1-2% PER DAY (more in warmer weather). The computers in your car constantly draw a small amount of power; that’s in addition to the self-discharge rate. If you leave a modern car sitting unused for a month, you can expect a discharged and sulfated battery. If you’re not going to use your car, buy a battery maintainer (not a trickle charger).

• Clean your battery terminals. Corroded terminals create high resistance and that reduces the effectiveness of your alternator.

©, 2019 Rick Muscoplat

Posted on by Rick Muscoplat


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