I'm not answering the questions you asked, but even a disconnected battery
will self-discharge. How quickly depends on the battery
chemistry and temperature, but I suggest leaving at least one of your panels
connected (through a charge controller) to keep the batteries
Of course if you will be using shore-power then you can cover or remove the panels
. Solar panels
do degrade over time (or so I am told), but for what it's worth mine have been out in the sun for fifteen years now with no significant reduction in output.