Well, like everything else having to do with lead acid batteries, regarding those open circuit voltage charts shown earlier in this thread ... "it depends": My special 90 amp hour Optima Yellow Top AGM battery has always shown around 13.1 volts on it's terminals after fully charging it and then measuring the voltage days afterwards. Right now it reads 12.89 volts terminal voltage after being used all night for my CPAP machine several weekends ago on a trip.
Perhaps all AGM batteries are not created equal.