What Is Sulphation In Batteries?

Sulphation refers to the formation of hard, crystalline lead sulfate deposits on lead-acid battery plates during discharge, which fail to dissolve during recharging. This irreversible buildup increases internal resistance, reduces capacity, and shortens lifespan. Common causes include undercharging, prolonged storage at low charge, or high temperatures. Prevention involves regular full charging, maintenance cycles, and storage at 100% state-of-charge with temperature control.

What causes sulphation in batteries?

Sulphation occurs when lead-acid batteries are left partially charged or idle, allowing lead sulfate crystals to harden. Key triggers include undercharging (below 12.4V for 12V batteries), electrolyte stratification, and temperatures above 27°C. Deep discharges below 50% capacity accelerate crystal growth, permanently reducing active material.

When a battery discharges, lead (Pb) and lead dioxide (PbO₂) react with sulfuric acid to form lead sulfate (PbSO₄). Normally, this reverses during charging. However, if the battery sits at ≤75% charge for weeks, these crystals grow larger and lose reactivity. Pro Tip: Use a maintenance charger delivering 13.6V–13.8V during storage to prevent sulfate formation. For example, marine batteries stored over winter without charging often lose 30% capacity within 6 months due to sulphation.

Transitional Phrase: Beyond voltage considerations, electrolyte stratification—where acid concentration varies between plate layers—also accelerates sulphation. Practically speaking, periodic equalization charges at 15V–15.5V (for 12V) can remix electrolytes. But what happens if stratification isn’t addressed? The lower battery sections sulfate irreversibly.

How does sulphation affect battery performance?

Sulphated batteries exhibit reduced capacity, slower charging, and voltage drops under load. Internal resistance can spike by 200%–400%, causing overheating. Cranking amps in automotive batteries may drop 50%, failing to start engines in cold weather.

As sulfate crystals coat plates, they block active material from participating in charge-discharge cycles. This lowers the battery’s effective surface area, cutting capacity. A 100Ah battery with moderate sulphation might deliver only 60Ah. Pro Tip: Test internal resistance monthly—a jump from 5mΩ to 20mΩ indicates severe sulphation. For instance, forklift batteries suffering 20% capacity loss often show voltage sag from 48V to 42V under load.

Transitional Phrase: Beyond capacity loss, sulphation increases charge times. A healthy battery reaching 80% charge in 4 hours might take 7+ hours when sulphated. Why? The hardened sulfate layers impede ion flow, forcing chargers to prolong absorption phases. Real-world example: Solar storage batteries in off-grid systems lose 1%/day in capacity if sulphation isn’t managed.

Can sulphation be reversed?

Mild sulphation is reversible using desulfation chargers with pulse or high-frequency ripple currents. These methods break crystals into smaller, reactive particles. Severe cases require replacing plates or the entire battery. Success depends on crystal size—particles >1μm are often permanent.

Desulfation techniques include:

• Pulse Charging: 2Hz–10kHz pulses resonate crystals, fragmenting them.
• Controlled Overcharging: 15.5V–16V (for 12V) dissolves small sulfates but risks corrosion.

Pro Tip: For AGM batteries, use only manufacturer-approved pulse chargers—excessive ripple currents can dry out separators. Example: A 12V car battery with 20% capacity recovery after 48-hour desulfation charging. However, if voltage stays below 10.5V during attempts, the battery is unrecoverable.

Transitional Phrase: While reversal is possible, it’s time-sensitive. Batteries sulfated for >6 months rarely recover fully. So, is it cost-effective? For industrial batteries costing $200+, yes. For $50 automotive units, replacement often makes sense.

Battery Expert Insight

FAQs