What size alternator do I need to power the AQ2200 amplifier and 2 HDC318's?

Im looking at putting a single AQ2200D amplifier in a Mercury Mountaineer (1998) to power 2 Hdc318's. I know that the current alternator probably doesn't create enough power to give the amplifier the amperage it needs. So should I buy an extra battery (kinetik, optima) or should I buy a new alternator (200, 250 amperage?) ?