Chassis battery dead

My 7 watt solar battery tender setup has worked flawlessly for 5  months now. 
I stick 2 of these Coleman 3.5W panels inside the windshield and plug them into both 12V  dash sockets. When it's time to get out and play they stow in  the seatback pockets inside padded 10 inch  tablet/laptop sleeves .https://www.menards.com/main/electrical/generators-alternative-power-generation/solar-power/coleman-reg-3-5-watt-12-volt-solar-charger-panel/58104/p-1444444200919.htm

7w/12v = .58A , not as good as the .75A Deltran Battery Tender Jr. spec. that I used as a benchmark, but it does the job and shuts off automatically every night too