I’m basically a day sailor but we’re contemplating a cruise around Lake Michigan this summer. I have two batteries on the boat connected to a selector switch and when I go out I alternate batteries daily. Batteries are fully charged overnight in the slip. I don’t use much electricity, an autopilot and multifunction display for chart, and GPS info. Last year I discovered that after a day of autopilot use occasionally and the other items all day, the battery I was on wouldn’t turn over the engine. I replaced both batteries and I’m thinking I need a battery monitor. I’m wondering though, do I need a separate battery monitor for each battery or will one monitor work. I’ve searched for wiring diagrams but can’t find what I think I’m looking for. Thinking about a Victron or Balmar but don’t really know what I need.