I'm humbled by your reply...I'm no expert but I try to learn from others and research before I make any changes
I'm sure from experience that overcharging batteries is as big a killer as undercharging. It all needs to be balanced.
And it seems to me that everything may seem fine for a while and then batteries suddenly fail because .?..
Your 300W solar direct to the batteries would have been the killer I'm sure....maybe you would have survived if you hadn't connected to shore power?
Everything needs to be regulated.....perhaps you need a solar mppt with bigger capacity do you can coonnectall the solar through it?
With our 6v AGMs one thing I did that seems to have maintained status quo was to wire in battery balancers on each bank to ensure that the voltage across each 6V battery was the same..we have 3 of them one for each series bank..I bought them from a chinese co. on alibaba...4 years out we see no loss in capacity...yet
I have to say I'm impressed with how far you've traveled since your start...well done mate.
Elyse SM437 Vuda Pt Fiji