Yah, there will be a drop in voltage when the starter load is engaged. This is due to the high current coursing through wiring, connections, battery impedance, and original battery source voltage and condition. My described voltage "collapse" was seeing the Lane voltage tape that I display on the Dynon well into the Yellow range. With my latest setup, the voltage drop is minimal.
There is a lot of information on Odyssey AGM batteries here:
AMER-EN-TM-ODY.pdf (odysseybattery.com)
You must use a charger designed for AGM and not just flooded Lead Acid batteries. The referenced manual states that you need to supply 40% of the rated current to charge a fully discharged battery. So in the case of your battery that would mean 40% of 16 AHr or 6.4 Amps. So the 8 A, AGM setting on this charger should work:
Amazon.com: BatteryMINDer 128CEC2: 12 Volt-2/4/8 AMP Lead Acid Battery Charger, Lithium (LiFePO4) Battery Maintainer, and Battery Desulfator : Automotive
Note that there are other references that say 10% to 25% of the battery AHr rating is sufficient.
In actual use, the battery is never really being charged from a highly discharged state. The manual states that a "maintenance" regime to keep the battery topped off is suitable (0.5 to 1.5 amp range). I've been using the 2 Amp version of the Battery Minder AGM charger with good results.
What charger are you presently using?
d.
