Do I need another battery??

I have 2 Rockford He2 10's and will be running them on a MA Audio 3600W(@.5 ohm) but the specs say it pushes 400w x 2 RMS at 4ohm. I will run it at 4ohm. Also a 100 x 4 crossfire amp pushing two pairs of 6 1/2 Sony Explods on the tower. Am I going to need to upgrade alternators or add a battery.

P.S. I have all of this stuff around the house (all but the sony's explods) The two subs, both amps etc. all the wires. I think it will sound real good in the boat.

Im not running half of what you have and I have 2 batteries. If you use your stereo without the motor running at all, run 2 batteries. For peace of mind, just in case. Nothing worse to be stranded on the water with a dead battery. And its a bit difficult to push start a boat.....