To understand just how reconditioning lead-acid batteries works, you need to fully understand just how the batteries themselves work. The lead-acid battery consists of plates of lead that are coated with lead oxide, and which are bathed in sulfuric acid.
When the battery puts out energy, lead sulfate forms on the plates of the battery, and what remains in the liquid is not sulfuric acid, but distilled water. When you charge the battery, this process is reversed, and the lead sulfate breaks down, leaving just the lead plates and the lead oxide, while the liquid turns into sulfuric acid again.
This is how things work in an operational battery.
However, in a battery that hasn't been charged for some time, or which has been discharged completely and then left in that state, the lead sulfate that is formed on the plates actually crystallizes. This is disastrous for the battery because, when a charging current is applied to a battery in this state, the lead sulfate does not break down. This effectively makes it impossible to charge the battery, and the battery is considered dead.
At this point, most people throw out the battery. However, what many people do not know, is that it is not necessary to throw out the battery at this point, and that it is actually possible to break down the lead sulfate to make the battery operational once more.
But is de-sulfating a battery a very complex process, and difficult to do?
Not at all. You just have to be careful, because the acid in the battery is really quite corrosive. You need to use a pair of long rubber gloves and protective glasses for the eyes before beginning the de-sulfation process. You also need to do the de-sulfation on a concrete slab or stone floor, as the acid is corrosive and might stain a floor that is susceptible to acid. It must also never be done on bare mud outdoors, as the acid must not be allowed to get into the soil.
The process is very elementary.
You need to take three or four liters of distilled water, and heat it until it is almost boiling. Now, toss in about ten teaspoons of Epsom salt and stir the liquid vigorously to make sure the salts are dissolved.
Empty the acid from the cells of your battery and pour in the Epsom salt mixture.
The Epsom salt mixture will break down the lead sulfate, and return your battery to operational condition. Having replaced the plugs on each cell, attach the battery to a charger and set the charger for high amperes. Older chargers actually work better at this process.
Keep the battery attached to the charger, and take a reading every hour or so (after detaching the battery) to monitor the charging process. The charging process could be done with rather quickly, or in some cases, could take as much as fourteen hours. Once it is done, and the battery is charged, you need to apply a load to the battery to discharge it completely. Once it is discharged, you need to charge it once more, while applying a low steady current this time around.
At this point, the battery may be considered operational.