I'm thinking for my own piece of mind, that I will add a second battery to run my sound system and isolate it from the cranking battery. I cannot find the output of the 4-Tec engines, so do I need the 60amp or the 120amp kit with ACR? And for those of you who have done this, does it charge both batteries from the magnetos of the 4-Tecs or only when an external charger is applied?