When I started looking at this ~20 yrs ago, there was only 1 website devoted to the principle of LA battery desulphation. For the life of me I can't find it ATM, it will be in one of my old archived HD's.
At the time IIRC it was based on a patent that was then explored to asses the science behind it.
Sulphation is a normal part of the charge-discharge process, it being reduced with charging as the sulpher is transfered back into the electrolyte, that then increases the SG.
Yep basic stuff.
But as a battery ages it's capacity reduces, WHY?
There was discussion of the sulpher bonds that form on the plates, that in time reduces the available plate area and reduces battery capacity.
These sulpher bonds are of some complexity, the simplist removed by just charging.
Others levels of bonds can be reduced with an OV charge of 15V or more.
The remaing are what Desulphation addresses.
This is not simple science, there are so many factors that affect battery life, the natural ageing process through use being only one of them.
Attempts to recover failing batteries bring mixed results and IME desulphation is best applied as a maintenence measure to extend battery life.
For the doubters:
A self powered desulphator WILL increase OC battery voltage after a period of application.
EVEN THOUGH THE DESULPHATOR HAS CONSUMED CURRENT FROM THE BATTERY.
AND battery electrolyte SG WILL rise also.
Now tell me it's