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.