Michelb I have found the same thing. I have a 15v nominal that I always tilted into the sun in similar weather to yours and using only it above normal converter or alternator charging for battery, got 10 years service out of more than one.
A healthy single battery seems quite happy with some of the 5w squares.
I used to alternate mine between the chassis or house battery each visit to the RV.
In Texas it will keep up a group 24 battery, even 30% shade blocked but tilted into the sun. Batteries with a low self discharge don't take much if you totally eliminate parasitic draws.
Jim
