I am about to make some major purchases for fishfinders and trolling motor. Hbird 899 and I want ipilot or link. I have a G3 60 hp 17.5 foot boat. Do I really need 80lb 24 volt unit for this size boat? I Spider rig mostly but I am going to try my hand at cranks soon. Would a terrova 55 12v with two battery fur longer life work ?