RV Batteries

Your RV (car alternator) will not fully charge AGM batteries.

A good solar controller will.

Fully charged for most AGM batteries is 12.8V (with no load).

AGM batteries can absorb more power if charged up to 14.4V which is called "absorption" mode, after it's completed the charger should go into ""float" mode (where the battery will drift back to 13.5V). You'll see on a large solar system times when the batteries can't take all of the available wattage, the regulator/charger should as it's #1 job protect the batteries.

Under load the voltage will decrease but you should try to avoid using more than 50% of the batteries capacity and set a minimum of 12V if you want to extend the life of the batteries. 

Put simply the deeper you discharge AGM the fewer charge/discharge cycles you'll get before you need a replacement. By using 30% capacity rather than 80% you could extend the life by years. Remember the target voltage is "no load' so don't worry if the volts sag a bit while you make the toast, (would start to worry under 11.3V) see what they bounce back to. 

deep_cycle_agm_batteries

Data below is from 3 X 120AH AGM 

Solar charge data log

*The (low) voltages above are while the system is under heavy load and not indicative of the true state of charge.