you mention having enough to require series and parallel connections to make up
a 48 volt bank?
so this is what i would do if i were you
get out a notebook and a pencil, you are going to need it anyway
start a log book for each battery, and each cell of each battery.
learn how to read the hydrometer, this is your friend and very necessary at this
point to find out what you have.
seperate the batteries into at least two groups, those that have fairly good and even specific gravities, and those with low or uneven specific gravities.
put all the good ones aside for a bit, you will be coming back to them soon.
take the poor condition ones and put them into a string that makes for 48 volts
make sure they are all full of distilled water, and put the string on a charger
and set it to equalize them. it might take 24 or more hours depending on the size of the cells and the capacity of the charger. keep an eye out for battery temperatures, stop charging if they get over about 100 degree's F and let them cool down. while they are cooling is a good time to switch over and begin charging the good string of batteries.
anyway keep watching the specific gravity and charging until they stop rising, after
which let them rest over night and recheck specific gravity and voltage.
if after you have done all this and you still have a battery or so with one cell that is just not responding, you may have to resort to more drastic measures, and
go back and apply more equalization charging to that battery.
some just won't come back, so you don't want to reintroduce bad or questionable ones into a string of otherwise good batteries, because that bad one will degrade the charging of all the others in the string and lead to undercharging and damage to other good cells.
when you are finally done and satisfied you have them all back in shape, log each batteries fully charged voltage and its fully charged specific gravity (each cell)
and date the entry. (let the cells rest for 24 hours before doing so)
then the next time you check up on your batteries you can tell if you are charging them correctly, if there is another bad battery starting to go south, or other issues taking place.
without your log, its a crap shoot and an excersize in memory.
bob g