If you put a capacitor in to suit the size of your amps it will take the burdon off the battery and alternator. Your battery will last longer too. If you continue to overload the battery it will eventually damage it too much.
I put a 1.2 Farrod Cap in for two amps (a 4 channel and a 2 channel amp) and never had any issues.
caraudioaustralia.com. You would be best to check there is a dedicated thick power cable to the amps, and you may need to uograde to a decent sound specific deep cycle battery. About $150. Check the tutorial questions for info there, or post the question, it's a good site for answers like this.