I realize this isn't EXACTLY on topic but I feel it is in the spirit
of desulfating. My question is where do you get your batteries to work
on? Or more specifically where can you get very cheap batteries to
try and revive? Call up auto shops? Talk to recyclers? How about the
nice big ones like forklift batteries?

Say you have a source of batteries, such as several old batteries
waiting to be recycled how do you test them to see if there are good
enough to desulfate? I have heard about shorted cell and a minimum
voltage, bulging cases etc. I have also read about people bringing
these exact ones back from the dead, though it's hit or miss. How do
you test them quickly, without charging. A conductance test? Just a
simple "pop the tops and look?" Multimeter?

I have a few old AGM 4Ah batteries that read either -0.5v or very low
that seem to be OK so far after watering/charging/desulfating (still
too early to tell I think) that failed many of these tests, contrary
to the general rules.

Very curious to hear your replies.