A friend of mine has "de-sulfated" (?) old batteries & allegedly brought them back into good condition-- some sort of device was involved
I've seen these- some of 'em apply a higher than normal charge voltage for a short period of time, others superimpose an AC voltage onto the normal charging current in the hopes of "punching through" the sulfation layer. I was also told (by a tech rep at Gill batteries, no less) to charge my G35 at a 10 amp rate one time only to reduce sulfation.
I've tried several of these approaches, with mixed success, but have not seen any real science to support any of these methods. I definitely prefer the idea of keeping the battery well maintained in the first place, through electrolyte replenishing and trickle charging (Battery Tender) when not used often.