The sulfuric acid in the battery combines with the lead plates to make lead sulfide; it can be white or yellow, depending on the oxidation state of the sulfide.
The ***** about it is the sulfate is bigger than the lead, so it pushes everything apart, causing pieces to fall off, and plates to short, causing dead cells.
Never use tap water in a battery, only distilled water (NOT drinkable water. the minerals in the water will kill a battery.)
Lead acid cells are 2.2V apiece when charged; they are not supposed to be discharged below 2V per cell. Our batteries have 6 cells, for 13.2V nominal when charged, 12V when discharged.
The (Best) chargers use a unregulated, rectified, pulsating DC voltage to charge; it peaks about 16V on the standard setting, less on the 2A setting. There are expensive chargers available that will 'quick charge' a battery: Don't use them on lead acid batteries; other battery types handle that better. Good quality, old-school, with a big honkin' transformer is the way to go.
The 200A setting is about 24V peak, if yours is like mine. Don't use that for long; only to get a battery to accept a charge if it won't at all. eventually, it will cause more sulfation, not less.(too much energy, wrong reaction)
The chemical reaction in our batteries is reversible within limits.
a good battery, charged at 1/20C, where C is the Amp/Hour capacity of the battery, will typically charge in 20 hours. The military determined this 60-70 years ago, the only things that have changed is the manufacturers of the batteries. charging faster is possible, but the tradeoff is battery lifetime.
An equalizing charge will eat the sulphation off the battery plates, if they aren't damaged, and this happens when the battery is said to be 'gassing freely'. This means a continuous stream of Hydrogen gas is being generated at the plates, AFTER reaching full charge. Since this eats water, the water level must be checked regularly; if the top of the plates get exposed to air, different reactions take place, not good, and NOT REVERSABLE. The battery will also be warm; if it is hot to the touch, it is charging too fast. Turn down the charger, or just let it cool for a couple of hours. Refill with water at the same time.
Never add water to a hot battery. It can come out violently, with acid in the mix.
Never wear good clothes around where you are messing with a battery; they will be full of holes, even if you think you didn't get any on you.
Since your battery is in the fairly decent voltage range, and doesn't seem to have a dead cell, I'd keep charging it. Keep an eye on the water, make sure it doesn't get too hot. If it gets too warm, too fast, discharge it with a light, (put in car, turn lights on, if nothing else) and try charging again. Time the discharge time; if it increases as you charge/discharge, then you can definately bring it back.
I've got a UPS for my computers (bought surplus), that provides a 50mA trickle charge to the batteries connected to it. It's made for gel cells, but it brought back a dead motorcycle battery in about a month...it will also boil a cycle batt when the lights go out; now I have a deep cycle marine battery on it...Hope it can fix it.
Hope this helps...I've saved a bunch of money this way over the years...
I do not believe in the newer tech batteries on the market; The main problem is the way they all 'immobilize' the acid, by gelling it, or absorbing it in a matrix. Not letting it mix makes a local deficit of acid, or water, where it needs it. If the electrolyte is liquid, then movement and convection currents keep the electrolyte mixed, and fresh, allowing greater current capability.
Sure, they will work upside down, but if I'm upside down, that's the least of my problems...