Came across this article from Elektor Electronics Magazine - November 2004 on the project for building a car battery desulfator.
http://notes.ump.edu.my/fkee/e-Magazine/Elektor%202004/Articles/E/e04b020.pdf
Extract from the article :-
Sulphation
The capacity of a lead-acid battery gradually decreases during its service life due to normal wear and tear, for a variety of reasons. However, the aging process is considerably accelerated if an uncharged battery is stored for longer than a week at a temperature below 10 ?C or remains unused (while charged) for an extended length of time. That?s because in such situations, a layer of nonconductive lead sulphate (PbSO4) forms on and around the electrodes. This reduces the effective surface area of the electrodes, thus decreasing the capacity of the battery. This process is difficult or impossible to reverse by normal charging and discharging.
However, it is possible to break down sulphate crystals into lead and sulphuric acid by using high (or very high) charging currents. This method can be used to restore at least part of the lost capacity (see ?Lead-acid battery revitaliser? in the September 2001 issue). Still, it?s better to prevent the formation of sulphate. One way to do this is to periodically apply a load to the idle battery. The circuit described in this article is especially suitable for this purpose.
http://notes.ump.edu.my/fkee/e-Magazine/Elektor%202004/Articles/E/e04b020.pdf
Extract from the article :-
Sulphation
The capacity of a lead-acid battery gradually decreases during its service life due to normal wear and tear, for a variety of reasons. However, the aging process is considerably accelerated if an uncharged battery is stored for longer than a week at a temperature below 10 ?C or remains unused (while charged) for an extended length of time. That?s because in such situations, a layer of nonconductive lead sulphate (PbSO4) forms on and around the electrodes. This reduces the effective surface area of the electrodes, thus decreasing the capacity of the battery. This process is difficult or impossible to reverse by normal charging and discharging.
However, it is possible to break down sulphate crystals into lead and sulphuric acid by using high (or very high) charging currents. This method can be used to restore at least part of the lost capacity (see ?Lead-acid battery revitaliser? in the September 2001 issue). Still, it?s better to prevent the formation of sulphate. One way to do this is to periodically apply a load to the idle battery. The circuit described in this article is especially suitable for this purpose.
