Desulfation in batteries

Sulfation is a phenomenon which occurs in lead acid batteries.  If a lead acid battery is kept unused for long periods of time or kept in a low charge condition, the lead sulphate in the electrode solidifies and forms a crystalline layer. 

This crystalline layer reduces the active surface in the electrode.  This results in reduced capacity.  The battery gets drained faster.

Sulfation can be classified into two stages. The reversible stage where the deposits have not solidified and can be removed and the permanent stage, where the lead sulphate crystals have solidified into a permanent layer which cannot be removed.

Desulfation involves removing this layer of sulphate deposits.  This is done by charging the cell to a higher voltage. The temperature of the battery is also raised to enable the crystals to dissolve.

There are also several products in the market which claim to desulfate batteries by injecting a pulse in the shape of a specific waveform.  Such claims have not been verified and are met with skepticism from some quarters.

Sulfation can be prevented by charging batteries to the optimum level and to avoid keeping batteries in the discharged condition.