I figure I'd post this here as it applies to self sustenance. I revived an old deep cycle battery with epsom salt. Before it wouldn't hold a charge but now it's replaced the paddles in my Jon boat. I've also done a lot of online research on electronic desulfators & came across this: http://batteryminders.com/details.php?prod=12248
You can charge & desulfate up to six 12 volt batteries in parallel & also pair up 6 volt batteries in series. It basically works on every type lead acid & gel battery with the exception of aviation batteries. It won't overcharge & you can leave it on for practically forever. Here's the Q&A: http://www.boatelectric.com/battery_minder_faq.html
I plan on reviving as many junk batteries from the scrapyard as I can. Hope his helps anyone saving money, going off the grid, or.. making extra money. I don't keep useful info to myself.