Well ... going through the batteries I have desulphated I am finding more often than not that the capacity is way down. - Time to see if I can pin-point the cause and see if it can be practically remedied.
I would expect a 40 A/h battery to be able to deliver 5 A for at least 6 hours before the V dropped below 11.5 and consider it as good as new.
But I'm getting 1,2,3,4 and only one out of the five I've load-tested has lasted 5.
Those which only lasted an hour were all replete with dirty electrolyte. And so I am considering acting on an old plan of mine to rig up a device which will filter the electrolyte.
For all I know the plates themselves may have become solid due to heat at some stage in their service-lives? Anyway I'm testing every battery I have to see if I can become absoluely sure of the signs of a battery with very low capacity despite being desulphated. - But I'm hoping filtered electrolyte will help. I am also hoping that dirty electrolyte does not indicate a battery with plates that are at a stage where they will continue to shed plate material due to being permanently loosened by whatever process made them start losing plate material in the first place.