Charger voltage will be well above 12.8 volts (vehicle will be at least 13.8v) where both batteries are full using those numbers so I don't see how the AGM will only be at 80% ?? AGM is mostly a more efficient lead acid technology not really a different battery like lithium would be or am I missing something ?

__________________
1988 325is (purchased new) sold
2004 X5 3.0 2005 X3 2.5
2008 X5 3.0 (new to me)