I have experience with solar systems and am willing to help you out.
I have some questions.
1 - Are you charging through a solar charge controller?
2 - Is your system properly protected with fuses or DC Breakers?
2 - Do you have a way of measuring voltage and amperage?
3 - Is the wiring clean and corrosion free?
Hello Norah and thanks for the PM. I'll get back to you with more data when I get back from the boat in about 12 days.
To answer your questions:
1) Yes, I have a charge controller (regulator), but for the life of me, I can't remember the brand and model!
2) I have a switch and fuse on my main panel. I checked the fuse and the wiring at the switch. All OK.
3) Yes, I have a decent handheld voltmeter, but no way of measuring amps such as with a battery monitor. I also have a fishfinder that also gives the voltage of the battery and it's all over the place measuring 10v and then 12.5v and oscillating like mad. When I start the engine and the alternator is engaged the voltmeter gives me a steady reading of 13v to 14v (in my mind showing the batteries are being charged and the voltmeter function of the fishfinder is working properly).
4) I have checked the battery terminals, battery switch connections and connections at fuse panel. These all check out OK. I suppose my next step is to look at the panels and all other connections between there and the batteries (diodes, regulator etc).
I should add that the batteries charge fine with the alternator and hold a charge normally. They seem to almost discharge when hooked up to the panels.