I have a 1994 volvo penta v6 with two marine batteries (fairly new) on a perko switch. I have noticed that I get a hard start on my boat when it's on just one battery. But when switched to both batteries it cranks right up with no problems. After I shut down and switch to either battery it starts right up as usual. My voltage tach usually stays under 12 when idle and my horn never works. But when I give it gas and am cruising lake my voltage reads between 13-14 volts and my horn is loud and clear. All my connections on battery and perko switch are tight so what could be the problem??