They're likely dead. If you ran them flat and didn't recharge them for several months...with a load on them, it is likely that you killed them.
I'm stupid an lazy, please don't rub it in.
I let my 3 2-year-old Optima batteries run flat in a frozen boat all winter.
Now it seems like they're not holding a charge...can't tell for sure because the boatyard keeps unplugging my extension cord after I leave. But they're dead upon return, even though the do hold a charge for a while as evidenced by cabin lighting after I've been hanging out while the charger has been on for a few hours.
The charger is a good one, a Heart Interface inverter/charger combo, set to AGM appropriately.
Is there anything I can do to resussitate these batteries?
Is it likely that my mistreatment would kill 'em?
3 x $200 , yuck.
That statement in itself is inconclusive - were the flooded batteries that were equalized - done so after being treated by a desulfator? That is what your quoted statement leads me to believe. Some mock the aspirin trick on batteries and I can tell you - I have done it - it works (its a one or two shot deal but will get you to where you have to go)...granted you have to buy a new battery but it can get you where you have to go...And, after over 18 months of testing the little pulsers mentioned above (which are NOT chargers, by the way) -- including the PulseTech models, of which I own several -- I don't have much faith in their claims to work as desulfators and to restore lost capacity. We found that after over a year of "treatment" with these desulfators, and vigorous exercising of the flooded and gelled golf-cart batteries under test, very little change in capacity occured. However, the flooded batteries were equalized a couple of times, and exhibited a significant increase in capacity.