[alchemy]

depends on what your situation and need is and how much money you have to throw around. I like long charges but not that long. I have more problems with short charges. Yeh, disconnect them all them check the cells, and load test. Mine from my yamaha are 2012's and still going great. The abused ones from my CC I'm still playing with mainly because I like the challenge. I even go so far as dong a little "alchemy" on batteries sometimes and it works but I'm a chemist too and you need diligent scientific-like skills and it's just too much to explain. For example sometimes you do need acid, especially with very old batteries but usually people who do that make them worse because more acid will produce more sulfate crystals too, the main killer of batteries. So, there is some diligent calculation and other considerations that need done with stuff like that. Epson salts imo is only good to have a charge median to try to buzz the plates off. Baking soda is the same, it's an attempt to fizz the plates off to remove sulfate. More experienced people used special adjustable chargers and pure water pressure to knock sulfate off. I have a last resort method which will work every time unless the plates are damaged but it's usually too time consuming. Those are the one extreme for you as for "how much time." If someone had a business doing restoration it might be practical but for guys like me it's just maybe a hobby or challenge.
I'd like to find some facts on the "mixing" factor fairtax rightly mentions. I want to find some science on that some day when I get time unless someone knows but I think about that a lot. Until then I'd rather have my batteries as close to the same as possible. I just put in two new batteries with the 6 1/2 year old ones hoping I could get a couple more similar ones to match before I ruin them. They were in my 36V cart so I had to add two. The difference is 6.45V on the new ones to 6.38 on the old. Something is dragging them down over 5 days from 50.9 to 50.6 just sitting with the mains disconnected. I assume that may be what it is.