The alternator is not designed for AGM type batteries. The charging profile is not proper and will kill an AGM battery prematurely. If you consider the added expense of an AGM there are no benefits to using one. A good, nationally branded lead-acid battery will easily last 5-7 years depending on how you take care of it. Interstate is a good brand. Never let a battery go completely dead. Never let it freeze. Keep it charged when not in use. Use a Battery Tender (or other smart trickle charger) for 1 day a month if you aren't actively using the car.