what and how many batteries?

i have 1600 watts of solar panels.each one is supposed to produce 21 volts.i have them grouped to produce 84 volts times 4.at 8.00 am they were producing 50 volts.ive seen them close to 80.i have a renogy MPPT solar charge controller to charge my 4 walmart rv marine batteries.question one is do i keep the older batteries tied in when they get weak?are 4 batteries at varying voltages better than two at peak voltage?what i would like is enough MAINTAINANCE FREE batteries to save ALL the power the solar panels produce because i forget to add water to them.id like to buy enough maintainance free batteries using the government rebate program to grab ALL the output from the solar panels.i hope to power parts of my home from the solar panels.all im using them for now is a few night lights and to run a attic ventilater on hot days.btw right now my voltage is 80 volts[2.27 pm]and my 4 batteries are at 14 volts.still four hours of daylight.