Reconditioning a heavy duty truck battery, Will it work?

Pulled the 3 heavy duty (expensive) batteries from my dump truck and decided to try to recondition them with a smart charger that has a recondition mode.All 3 got pulled down to less than 4 volts when I left the PTO switch on for a month or so:my own dang fault. Anyway the replacements are around $450.00 for all 3 so it's worth my time to try to recondition them. Explain in my simple way the smart charger,a dumb charger,an electronic battery tester and an old analog tester (more military surplus I picked up for next to nothing).After the 1st 24 hours in recondition mode it looks like I might be doing some good:voltage creeping up but still showing sulfated. Will update whether it works or not.

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