[DonRotolo]

There are two "kinds" of lead sulphate, which I have come to call "soft crystal" and "Hard crystal". Soft crystal can be worn away by a certain charging pattern, and this is what I feel these "desulphators" can attack. Hard crystals cannot be broken down, and thus are permanent.

Over time, my theory is that the soft turns to hard as the crystal structure has time to stabilize. Think of the atoms lining up a little bit better.

This may be a lot of hooey, but with 20+ years in the lead-acid battery world, this is what I have observed. The above are opinions, not necessarily facts.

By the way, it is a fact that lead-acid batteries' failure mechanism is through sulphation. Lead oxide (the battery plates are coated with a paste of this), as the battery is discharged, turns into lead sulphate, drawing the sulphur from the sulphuric acid electrolyte (and freeing electrons in the process). Recharging pulls the sulphur atoms from the lead and puts them back into the electrolyte.

Or, said another way: Leaving your lead-acid battery discharged for any time at all leads to permanent, irreversible damage. Keep a lead-acid battery at 100% charge and it will last decades. A reasonable time between charge cycles is 2-3 months.