according to rolls/surrette engineers, (a maker of flooded lead acid cells)
they dry charge their cells, and then wash them down, dry the plates and assemble the battery
the battery can be stored for 5 years in this state without any degradation and that is warranted
i press them because i wanted to have a shelf life of 10 years, i was told that they would expect some degradation
of capacity, but not much
after 28 years i would expect some serious degradation, because of oxidation and hardening of the pasted plates
this should get better after maybe 50 charge/discharge cycles.
in years past, dry charged cells, were flushed with nitrogen and sealed with little plastic caps that you had to dig out
under the watering caps, they popped out with a whoosh sound, you added acid and put them on a charger for a couple hours
before putting them in the vehicle, although they generally would start the vehicle right after being juiced up.
i really believe you just need to cycle these things pretty hard a few dozen times, and chart their progress, my bet is they come back to usable if not original capacity after maybe 50 cycles or so.
even if you don't plan on deep cycling them in you application, it is important that you do so at first, this opens up the pores, reactivates the pasted plates and forces them to do their thing, otherwise light cycling really doesn't get the action working well.
rolls/surrette states that their batteries will not deliver their rated capacity until after a few dozen deep discharge/recharge cycles.
i can't imagine any other flooded lead acid battery being any different, especially after sitting dry for so long.
bob g