I found this post on a battery forum and I'm wondering if anyone here had ever come across this method ot used it themselves?
I have a large Deep cycle battery with one defective cell and it only holds charge for a week before dropping to 11V

"With regard to ex-Telecom batteries .. they are often 'sulphated' by the time you buy them and will probably need rejuvenating. You can use an electronic device to get rid of surface sulphation, but it doesn't get rid of sulphation that is buried in the porous lead plates. Here's a method routinely used by Australian and American military to revive 'dead' lead-acid batteries. First, buy yourself some 'Glauber's Salts' about a kilo or two should do it for a large truck battery. Dissolve the Glaubers in distilled (battery) water. It helps to warm it up a bit. Glaubers is pretty benign. It won't go 'boom' on you. Next empty out the old acid and get rid of it. (Wood fire ash added slowly will do this, but DO IT SLOWLY! Make sure your face and skin is protected from splashes of acid) Fill the battery with Glaubers solution and charge it until it starts to 'gas'. Sometimes it wont gas at all on the first few attempts, just persevere. After each charge cycle, discard the Glaubers (it's great foor making your citrus taste sweeter. Just dilute it ten to one and pour it around your citrus drip line) and after you have rinsed out the battery with distilled water ('Battery water' ..de-ionised) replace with fresh Glaubers and repeat the charge process. Four or five times through this sequence will revive even the deadest of lead-acid batteries. Finally, replace the Glaubers after the rinse out with fresh acid. Then add roughly a tablespoon full of Glaubers to each cell of your truck battery and charge it up. It will be as good as new. The reason for rinsing out at each turn is to wash out any flakes of sulphate. TAKE CARE. ACID IS DANGEROUS TO HANDLE. KEEP KIDS AND ANIMALS AWAY. I REFUSE TO BE RESPONSIBLE FOR YOUR LACK OF COMMON SENSE IF YOU INJURE YOURSELF OR SOMEONE ELSE. BE IT ON YOUR HEAD."


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