There are a couple of tricks to getting a sulfated battery to take a charge. One is to add a very small amount of fresh acid, not more than an ounce or so, to each cell before connecting the charger. It's necessary to get a small amount of current flowing to begin breaking down the lead sulfate and get the acid back into solution. If you can turn the voltage up enough to get a charge current of 5 to 10 amps, the sulfated plates will begin to re-configure back to lead on the negative plate, and lead dioxide on the positive, with the electrolyte converting back to sulfuric acid. As the charge progresses, the acid will gain strength.
Lead sulfate forming at both positive and negative plates is a normal byproduct of a battery discharging, but it is a spongy material initially. At that stage, it re-dissolves easily as charge current is applied. If the battery stays discharged for a time, the sulfate converts to a hard, stable crystalline form which is very hard to dissolve. Charge the battery until the specific gravity stops increasing, then run it all the way down with a headlight bulb or other slow, continuous discharge. Slow charge again, discharge, recharge, etc. If the battery is salvageable, it should begin holding a partial charge about the 5th. or 6th. charge/discharge cycle. It might take 10 or more cycles to get full capacity, if at all. Normal full-charge specific gravity is about 1.265 to 1.300, measured with a hydrometer. Discharged specific gravity will be close to 1.000, same as water. Once the battery starts accepting a charge, DO NOT add more acid. The acid trapped in the plates will re-combine with the water to give the specific gravity rise needed.
Jerry
Edit: I recovered a 6V battery that had been sitting in a stored car since 1981, about a year ago! Not perfect, but good enough to start a 216 without boosting! 12 volt batteries don't usually do as well for some reason.
Jerry
Last edited by Hotrod Lincoln; 06/08/2010 6:25 PM.
