Why Do Lead-Acid Batteries Fail Prematurely?

A standard lead-acid battery has a typical life span of 3 to 5 years, yet many users experience backup issues within just 2 to 2.5 years. Why does this happen?

While there can be several causes for reduced backup time, in over 80% of early battery failures in Pakistan, sulfation is the primary culprit. Once you understand how sulfation works, protecting your battery becomes much easier.

What is Sulfation?

Sulfation refers to the accumulation of lead sulfate (PbSO₄) crystals on battery plates. It’s a natural process that happens during battery discharge. As the battery discharges, lead sulfate sticks to the plates. When the battery recharges, this sulfate dissolves back into the acid.

The problem arises when this layer hardens and no longer dissolves properly. It slows down the flow of current between the plates and the acid, preventing the battery from fully charging. This results in reduced backup time.

At this point, people assume the battery’s life is over. But in reality, the plates are still healthy — only a hardened sulfate layer is blocking them. If removed, the battery's performance can be restored.

What Causes Sulfation?

Here are the 4 major causes of sulfation in lead-acid batteries:

1. Using Tap Water Instead of Zero TDS Water

Many people use regular tap water to refill batteries. Tap water contains minerals and salts that accelerate the sulfation process. Lead sulfate builds up faster and is harder to dissolve, shortening battery life to just 1–2 years.

🔧 Solution:

Always use battery-grade distilled water with zero TDS (Total Dissolved Solids). Prefer water from reputed battery manufacturers like AGS. If not available, use AC drainage water, though it still has ~40 TDS.

2. Not Fully Charging or Deep Discharging the Battery

If you don't fully charge the battery after it is discharged, the remaining lead sulfate hardens. This is a common issue with car and solar batteries, as driving or sunlight availability is inconsistent — especially in winter when batteries often don’t reach a full charge.

🔧 Solution:

Avoid discharging the battery below 20%, and fully recharge it at least once every 2 weeks (or once a month minimum).

3. Storing the Battery at High Temperatures

Batteries should be stored at room temperature (25°C) or lower. At 35°C, the self-discharge rate doubles, which drastically increases sulfation.

🔧 Solution:

Keep batteries in cool, ventilated areas away from direct sunlight or heat sources.

4. Neglecting Battery Water Levels

When the electrolyte level drops, battery plates become exposed and start drying out. This leads to hardened sulfate deposits, corrosion, and overheating. Sometimes, it can even cause the battery to burst.

🔧 Solution:

Check the water level every 15 days in hot areas, and at least once a month in cold regions. Never use tap water — stick to distilled or battery water only.

How to Know If Your Battery is Sulfated

If your lead-acid battery (used in UPS, solar, or cars) is less than 3 years old and showing a voltage below 12.4V, it is likely undercharged due to sulfation.

🧪 You can use a multimeter to test for sulfation or get it checked by a technician.

How to Fix a Sulfated Battery

Depending on how advanced the sulfation is, here are three solutions:

✅ Mild Sulfation:

Have the battery fully charged on a slow charger by a skilled technician. This helps dissolve lead sulfate back into the acid.

✅ Moderate Sulfation:

Use a battery desulfator or conditioner available in the market. These chemicals clean the plates and restore performance.

⚠️ Heavy Sulfation:

Use a special pulse charger that sends controlled pulses to break down hardened crystals. However, full backup may not be restored.

❗ Note: If the plates are broken, cells are dead, or the battery is over 5 years old, these methods won’t help much. To check for damaged plates, open the caps and inspect the bottom. If you see brown or black debris, the plates have broken and the battery needs replacement.