Understanding Sulphation in Lead-Acid Batteries: Causes, Types, and Signs
By the author of the Amazon Bestseller Book 'Batteries Demystified', Podcaster, & Expert in Lead Acid Battery Manufacturing Processes and Machines
Introduction
Welcome to this detailed explainer on a crucial topic that often determines the performance and lifespan of lead-acid batteries—Sulphation.
In this article, I aim to demystify what sulphation means, when it occurs, how to identify it, and why, in some cases, it is reversible, while in others, it proves fatal to your battery’s health.
What is Sulphation?
Sulphation refers to the formation of lead sulphate (PbSO₄) crystals on the battery plates. It is a natural part of the battery's chemistry, but it can turn into a problem under certain conditions.
There are three primary occasions when sulphation occurs in lead-acid batteries:
1. During regular charge-discharge cycles
2. When the battery is idle and undergoes self-discharge
3. Due to misuse, neglect, or abuse of the battery
1. Sulphation During Normal Operation
In a properly functioning lead-acid battery:
- Discharge causes both positive and negative plates to convert into lead sulphate.
- On recharging, these revert:
- Positive plates → Lead dioxide (PbO₂)
- Negative plates → Sponge lead (Pb)
This reversible reaction is essential to battery function and not harmful as long as the battery is cycled and appropriately maintained.
2. Sulphation Due to Idle Battery and Self-Discharge
When a battery remains idle for extended periods, self-discharge can lead to sulfation. However, this type of sulphation is generally reversible.
Example: During the lockdowns, many vehicle batteries lay unused and were found discharged. These were successfully revived using a bench charger or an external charger.
For large industrial batteries (e.g., forklifts or platform pallet trucks), low-current charging is used to prevent overheating.
- Especially in 48V or 72V battery systems, only a few cells may lag, necessitating slow, balanced charging.
3. Sulphation Due to Misuse or Neglect
This is the most damaging and often irreversible form of sulphation. It occurs when:
- Sulphuric acid is mistakenly used instead of water during topping up.
- The battery is left in a discharged state for too long.
- It is operated at continuously elevated temperatures beyond recommended limits.
- Lagging cells are ignored and not promptly repaired or replaced.
- The battery is not topped up regularly with distilled water.
What Happens Inside the Battery?
When plates are not fully immersed in the electrolyte due to poor maintenance:
- The top portions of plates don’t participate in chemical reactions.
- These exposed areas heat up, undergo irreversible sulphation, and become inactive.
- Such damage is visible during inspection: the top of the plate turns whitish, while the bottom remains normal.
- The battery’s performance drops significantly as a part of the plate no longer contributes to energy output.
These sulfate formations result in large, hard crystals, which are very different from the fine crystals formed during regular operation. These large sulphate crusts are difficult to remove, even in controlled environments.
How to Identify Sulphation?
Key indicators of sulphation include:
- Noticeable reduction in battery capacity
- Rapid voltage rise during charging
- Consistently low specific gravity in all cells
- Bulging of the battery container
Why bulging? Lead sulphate occupies a greater volume than active materials like lead dioxide or sponge lead, pushing against the cell walls and the battery’s outer casing.
To hear a podcast related to this topic of Sulphation, please click the link below:
Can Sulphated Batteries Be Revived?
- If sulphation is due to idle time, yes—it can be reversed with appropriate charging.
- If due to neglect or abuse, revival is very difficult—even for manufacturers.
Restoration requires expert intervention, is a time-consuming procedure, and offers no guarantee of success.
Some cells might respond, while others may not. In rare cases, the whole battery may be brought back to life.
In Conclusion
Sulphation is both a natural phenomenon and a dangerous fault, depending on the context. Regular maintenance, timely water top-up, correct operation temperature, and early fault detection can go a long way in preventing irreversible sulphation.