One thing I have learned of late researching RV batteries & solar charging systems is that different battery chemistries require different charging voltages. AGM requires a higher charging voltage than lead acid, and that is likely what has been at play with the Optima Blue Top (AGM) I have been running in my truck: the 12si alternator in it doesn't supply the higher voltage required by that battery, and consequently, the battery never gets fully charged.

A couple of months ago, I needed a battery charger to fill the hole between the Battery Tender and the Forney 60-amp roll-around charger/booster I have, so I bought (unintentionally) a charger with different charging programs for different chemistries. 24 hours later on the AGM setting, that Blue Top was fully charged for the first time in I don't know how long. This is when the light went on concerning charge voltage and that battery. I top it up occasionally now, and after every drive.