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.

Grant, you may have a bad battery. I just checked a group 27 Deka AGM we have on our shelf. The battery has a date code of March 2009. It has never been on a charger and shows 12.53v. They should be closer to 12.6v when fully charged and checked after a night of resting. It is a pain but you should disconnect all the batteries. Then charge and check them individually. Really it is best to have some sort of tester that can put a load on them. If you have access to a carbon pile you can use on of those. If you you are just going to use a voltmeter to test do the charge and then check them the next day after they have time to get rid of the surface charge.