I am thinking of getting a second battery to throw in the back but was wondering if it is going to be hard on my alternator, i also read that all i have to do is wire it just like a cap + to + then to the amp and then - to - then to the amp is this correct, Thanks alot.
No it doesn't hurt your alternator, but it also doesn't give you any more power. An HO alternator will.
What the extra battery will do is give you more power when you're running off the batteries (engine off). This is useful for competition but not enough to make an audible difference.
Also, when you wire batteries in parallel (the method you're talking about), they have to be the same brand/model.
Don't wire them together. You could use an isolator to have one battery for the audio system and one for the car, but thats not going to help your audio system any as it still only has one battery.
what exactly happens when you dont use the same batts? and also say you have a red top upfront and 2 yellow tops in the rear but mainly what happens with diff brands thanks
not mainly different brands, but different "types" of batteries. You want to keep wet with wet, dry with dry, and acid with acid, etc. As far as the red top up front, and yellows in the rear. That is a common battery setup. Theres no problem in that.