AGM Battery question's

A few month's ago a switched out my stock of AGM battery's in my boat. I was running Sea volt AGM 92 amp hr battery's. When I switch them out I upgraded to a larger more powerfull AGM battery. Again I went with Sea volt AGM's this time 105 amp hr battery's. These new larger more powerfull battery's don't seem to be holding voltage quite like my old battery's did. Any Idea's.
My old set up I would un plug the boat from the charger and the batterys would equalize and settel down to a voltage between 13 and 12.8 volt's. Now after unpluging the charger after reaching a full state of charge my bat's are s****ing at around 12.4 to 12.2 IMO somthings wrong. Do I have a bad battery. Im guessing I have to take out all my battery's and have them tested to find out if I have a dead cell in one thats dragging me down.