Carquest agm battery

[lance_98main]

I was at carquest today and they had an extreme agm battery, and it was 55ah for $135. I was wondering if they are any good or not. I have a regular battery up front and nothing in the back, and stock alt. I have an audioque 2200 d, and am soon going to be running either 1 18 or 4 12's. With the 18 i'll be wired at 1 ohm, with the 12's it will be 2 ohm. I love single sub setups. I was wondering if I bought one or two of these batteries if it would help keep me in the 13 volt range with stock alt. Or would i be better off just buying a bigger alt? Right now running my rf t1500 i drop to 13.1 while driving wired at 2 ohms, the lowest i've seen it is 12.5 while sitting idling giving a demo, with some c&s music. I also have a planet audio tq601 4 channel amp for my mids and highs, and 2 runs of 1/0. Thanks in advance for the help.