I only play it loud when wakeboarding or crusing. Lots of homes and boats on my lake and I am the type to consider others. I have not made the batteries break a sweat but am sure they would last all day floating at moderate levels. They will also last a long time in number of years both because they are AGM, I don’t fraw them way down amd I have a dual bank shore charger with shore power.
Think of the solar panels as weak trickle chargers. They help over a number of days. Do be careful executing any dvsr mods as how the solar panels are wired will mater and I don’t have a boat with the panels to test and advise. Given how the dvsr operates even with the mod I believe that the batteries should be of the same chemistry, size, and health when installed.
What one needs will all depend on how many watts they are going to consume and how loud it is played will affect consumption.
I always recommend researching AND understanding which it seems
@Lion is doing. I am sure you will end up with a great performing system.
One last piece is great connections make a big difference. Tinning the wire, fluxing the inside of the crimp, crimping and then reheating makes a great connection.