What is that simple procedure??
The VRLA batteries are subject to three principal failure modes. Any early failure is technically named PCL (Premature Capacity Loss).
The PCL-1 mode is caused from developing a passivation layer between the positive grid and the active material deposed on it. This has been solved by adding tin, silver or both to the positive plate, which act as a dopant.
The PCL-2 mode is another type of interconnecting layer failure; some PbO forms at the interface between the PbO2. PbO is a semiconductor which impede the recharging of the battery. This is more common in pure lead plate configuration (think of Cyclon / Enersys / Exide batteries).
The PCL-3 failure mode is the polarization of negative plate. This is when the oxygen cycle, necessary to recombine water in a sealed battery, becomes too strong. Normally, oxygen lands on the negative plate forming PbO, the H2SO4 electrolyte convert it to PbSO4, and then is treated as a the normal discharge product of a negative plate, effectively reforming water. Problem is when any charging current flowing thru the battery initiate the oxygen cycle, due to lowering of overpotential caused from impurities or overcharge.
There are other failure modes, and those are EOL modes (End Of Life), namely electrolyte dry-out, gravity stratification, plate shredding, negative top lead corrosion, negative plate dendrites. There is no indication of sulfation as a failure mode of a battery, as it is a normal phenomena.
How to recover? Recharge the battery. If any of the other PCL modes are not present, sulfation can be easily recovered.
Traditionally, a sulfated lead acid battery had to be left under float charge for months, in order to recover some capacity. Lately, better methods have been devised. Lead sulphate is a normal discharge product, initially slightly soluble in sulphuric acid. If the battery is left uncharged, the lead sulphate crystallise, converting from an amorphous state to a crystalline state. Since it is non-conductive electrically, battery doesn't seem to accept charge. In reality it will, in the range of few microamps, this is why will take months. The actual trend is to use high energy pulses, which produces a mechanical force that, in turn, fracture the sulphate crystals. The pulse has to have a current equal to the normal short-circuit current of the battery, and have a 1 microsecond duration every second. They uses large inductors and power MOSFETs.
If you type "desulfator" into Google, you will see a large offering of those gizmos. They are not officially endorsed by battery manufacturers, but they works. Due to the large market created from solar energy installations, which have to deal with chronically undercharged batteries (which are perennially sulfated), a desulfator proves a wise investment. Desulfator techniques are also used in specialised charger, like the Optimate4, which I use to keep charged and clean from PbSO4 the motorcycle batteries installed in my UPS (I don't use VRLA batteries for this purpose).
The real problem comes when the sulfation is aggregated to other PCL modes. The most common combination is Sulfation/PCL-2. Even this can be recovered, but you need to open the battery, as only dendrites and plate shredding are unrecoverable. If there is enough interest, I can prepare a recovery tutorial and present in its own thread.
Hope this helps.
Anthony