jsoceanlord, Don't let the guys scare you away...they really want to help...i think!...sounds like you have nothing set up now and would like to set up your solar panel to maintain a battery...
instead of taking home to recharge...lead acid would do, but it
sounds like you want a "deep cycle battery". As indicated above
you really must have a sense of your panel output and usage
before you can size...and remember you don't want to run battery down more than 50 % of capacity...for that will shorten
life of said battery. You did not mention starting a motor
lights...no power needed for motor
is ok...but simple
set up for nav lights is always a good idea...many a day sail has
ended up in moonlight...by the way(depending where you sail) if a small solar panel is your only source to recharge, you
may have to occasionally take your battery home to top off...
therefore you may still refer to it as a "portable" battery.