This boat has had this setup for a long time. Presumably your
charger is making amps!
You issue is the
monitor is not showing 100% against your expectation it would.
I guaranty the
monitor is not calibrated - It is not easy to do, so it doesn't get done.
You
batteries are likely old - their capacity is surely down. Look at it this way - what the monitor expects to see as full is no longer "full."
They may be fully charged, but they may not hold as many useable amps today - the monitor doesn't know that unless you tell it.
The first thing I would but before
solar is install a SmartGauge - I am convinced this is a much simpler device for assessing SOC for the average boater.