Battery Sulfation

What is battery sulfation?

What is battery sulfation?

How does battery sulfation occur?

Battery sulfation occurs when a battery is undercharged or deprived of a full charge. Every time we don’t complete a full charge,  it adds to the build-up of sulfates. What is battery sulfation? It is normal in a battery for small sulfate crystals to form during its use. This is normal & do not harm the battery.  However, if the battery is regularly not being charged fully, the amorphous lead sulfate converts to a crystalline that’s more stable and deposits itself on the negative plate. This tends to grow like all salt crystals and hinders the negative active material from taking part in the battery reactions completely.

Sulfation, particularly of the negative plate, is an important cause for the failure of the battery. Lead sulphate is slightly soluble in water (45mg/lit) and the solubility decreases with increasing concentration of acid above 1.05 Lead sulphate continuously dissolves and reprecipitates in a dynamic equilibrium with the dissolved species. Over a long period, when the battery is in idle storage, at an elevated temperature, this can result in the finely divided powdery lead sulphate to form to a hard caked crystalline form. A discharged battery suffers more such sulfation. The size of “ as discharged “ lead sulphate is about 1μm, after 8 days’ storage the size becomes 5 μm and after 5 months to 10 μm. The larger crystals are not readily recharged, resulting in loss of capacity. This irreversible formation of large, hard, caked lead sulphate is termed as Sulfation.

 This type of lead sulphate also increases the internal resistance of the battery.

What are the symptoms of sulfation?


  • Fall in capacity of the cell
  • Fall in electrolyte density
  • Higher charging voltage and poor charge acceptance
  • Early gassing
  • Bulking of active material and chunky shedding
  • Discolouration of plates and sandy/gritty feel to touch
how to remove sulfation in battery?

What are the effects of sulfation?

There are two types of sulfation, reversible & irreversible sulfation. If the battery is immediately serviced, reversible sulfation can be corrected by applying an overcharge to a fully charged battery to break up the crystals.

Permanent sulfation occurs when the battery is left discharged unattended for weeks or months. In this condition, the crystals grow to such a size that the negative plates appear white. It is very difficult to recover such sulfated batteries.

Causes of sulfation

  • leaving the battery discharged for long periods of time
  • the battery is frequently undercharged
  • Low electrolyte level or electrolyte level falls below the top of the plate
  • Battery storage at elevated temperatures
  • Absence of corrective action on lagging cells.
  • Topping up wrongly with acid electrolyte instead of DM water
  • High-temperature operations
  • Frequent undercharging or low float voltage
  • Stratification of electrolyte.
  • left to sit in hot climates accelerates the process 

How to prevent sulfation?

If you need to store the battery away for long periods of time, charge it fully first. Then plug it to a smart charger which will keep the battery on a low or float charge. This will ensure that the battery will not sulfate.

What is the blue powder on my battery terminals?

The white powder you see around the battery terminals is lead sulfates. When the terminals have copper inserts for better electrical conductivity the copper reacts with sulphuric acid to form copper sulfate. Anhydrous copper sulfates turn a luminescent bluish green. This can be simply washed away once a year with baking soda & water. Always keep the battery terminals clean & coated with a thin layer of petroleum jelly not grease.

How to Remove Sulfation From Batteries?

  1. Long charge with small currents: This method is recommended for low or early sulphation. The sulphated cells are topped up with distilled water. Charge at normal current till noticeable gassing stage. Give rest for half an hour and recharge at a tenth of the normal charging current till profuse gassing is observed. Again rest for 30 minutes. Recharge at the above low rate. This is repeated number of times till specific gravity and charging voltage of cells remain constant close to normal value. Minor adjustment to the required density level might be done.
  2. Charging with total distilled water replacement. : This is recommended for high sulphation levels recently. Discharge the cells fully to 1.7 V / cell. Drain out the electrolyte. And replace with distilled water. After soaking time of an hour, charge the cells at 2.3V/ cell. The initial charging current will be low and will slowly pick up. The density also slowly increases. When the density rises to 1.2, reduce the charging current to one-fifth of normal charging current to avoid heat up of cell. When gassing is profuse,& the gravity is steady stop the charge, rest for a short time and discharge at a low current say C20  to 1.75V/cell. This cycle is repeated until the reaches a near-normal level. Minor adjustments of density may be done and the cells put to normal service. 
  3. Deep discharge recovery: This may be useful for long-neglected cells. The cell is charged at a current equal to 0.2C and when the voltage of 2.4/cell has reached the current is reduced to 0.05C. When the voltage and attain a stable value, the charging is stopped and the cell rested for one hour. Again charging is continued at 0.05C amperes till steady state is reached (V & const) and gassing is high. Rest again for one hour. This type of charging alone with rest is repeated till gassing starts immediately on the initiation of charge. Now the cell is discharged after an hours’ rest at 0.02 C amps to a cut off voltage of 1.75. Rest for 2 hours. Repeat the charging alone with rest cycles as above and repeat discharge. About 7 to 8 cycles required for full restoration.  

What else is needed, to avoid sulfation?

Proper battery charging ensure long life of your investment. Batteries have become integral part of our lives. It is also the most expensive item to be requiring replacement once in 4 to 10 years as the design needs may be. It would be prudent to keep the battery properly charged regularly to avoid premature failures. Sulfation can be easily avoided.

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