I let the batteries sit a couple of days - voltages were still well up there in the 12.6 - 12.7 range.
Hydrometer showed SG readings on one battery with most cells at 1.175 and a couple at 1.200. Other battery had even split between 1.200 and 1.225. No obviously dead or shorted cells, but both with definitely lower SG than I would expect for fully charged batteries. Not sure what this means.. Bad hydrometer?
Brian suggested equalizing, but neither of my chargers has a button for 'equalize' - they're just your normal 10 amp, 3 stage chargers. Any suggestions?