you know that your car has a circuit to charge an AGM battery. An AGM battery needs a special LVC (Low Voltage Cutout) to protect it.
I installed an AGM battery in my basement some 7 years ago. I had to use a charger that was capable of charging AGM batteries. If I remember correctly, there are 4 different charging stages. These 4 charging cycles are different for AGM and Lead Acid batteries.
Best regards,
Alex