Tigers, family and friends,

My boat has 4 batteries connected in series. Each battery is rated 6v 300Ah. On my electrical panel is saying 600Ah. However, I can not see any starting battery. On the boat everything is working well (Tv, fridge lights, water pumps anchor etc..) and solar panels are charging and keeping batteries on 600Ah. If I use the boat everyday, engine starts easy, but if doing it on weekly basis engine is struggling due to low cranking amp. 1. Is it possible that stating battery is somewhere else on the boat (I can have a look around) and is slowly giving up? So far I found 4 batteries 6v 300Ah Lifeline GPL 6TC (bloody 1100 bucks each) and a regulator all under the bed and no other wires that could possibly lead to a starting battery.

2. Should I add 150 AMG battery to those 4 to give some more power. I do have a switch for starting engine battery or both, but there is not difference what every I put on.
A bit confusing here. Feels scary when engine is not reacting while the starting button is pushed. All batteries are connected to positive and negative terminals a bit further from batteries and I could just connect a new battery directly to this terminals to avoid connections between those 4 batteries. Any suggestions what is going on here?

Thanks tigers

Serb, having watched and contributed to your many learning experiences, I have to say that, in the most constructive and caring way, you obviously have no idea what you have in the way of electrics on your new boat (ie: four 6 volt batteries in series, I would be astounded if a hunter ran a 24 volt system) and for your sake and the safety of your family, you need to get a competent marine electrician to assess your electrical system and instruct you in it's operation BEFORE you make any additions or alterations.

Boats are an adventure. . Well done solving the battery issue, securing your disabled boat, clearing a tangled rope around the prop and giving the hull a clean while your down there. Quite an afternoons work.