System Turns Off??

Out on my boat yesterday (Glassy I might Ad) and if the volume on my radio was turned up loud the Head unit and amp for my tower speakers would turn off. Only running one battery (ever start deep cycle I think) for system 500x4 JL Audio amp four 100w Liquid audio 6.5's on tower, Four Sony 75w speakers off of the head unit. Also when I turn on the ballast pumps same problem. I think it is a battery or Alt. problem but Im not sure. What do ya'll think. Want to install Sub soon so any feedback would be great.