Just finished reading the post on extending battery life. The writer hit it on the head when he talked about pulse charging batteries. As a matter of fact there is a company out of Hayden, Idaho (in the American Redoubt) which makes microprocessor-controlled desulphating battery chargers. John Bedini has been designing these chargers for many years, and has now made them commercially available. His company is called Energenx.
I have three of his heavy duty chargers for use on Trojan batteries. The chargers have a charge cycle and a desulphate cycle where they charge and discharge several times to bring the life back to the battery. There is a lot of research behind his patented process.
As long as the battery is not physically damaged, and the specific gravity cell to cell is close to the same, then these chargers will restore life to your battery bank. Trojans are notorious for the center cell on the 6 volts dying first, and it has restored several of mine. – T.C. in The Pacific Northwest