I agree with Dan, and you have confirmed that they are scrap.
If you get enough capacity out of them to do what you need then keep using them. Let them boil at 14v, they may get better, just add water when needed and make sure nothing ignites the gas. ( keep terminals tight and keep all source of ignition away).
They may be incapable of high current discharge but you don't seem to want that so it should be fine.
If you want to spend money and effort you could try EDTA, it may help but don't expect much. You can try desulphators but again I have never seen one do any good.
They may improve with use but will never regain anything like their capacity.
As I said, if you can live with their limitations that's fine, if you really want batteries that work, ditch them and save a lot of wasted effort.
They will probably die from shorted plates caused by moss growth through the separators but until then you may get a few years of limited performance.
Flux