I'm almost + It's your chargers. Some of the newer electronic ones you can't make sparks by touching the terminals together, Explosion proof or some other safety feature. The old style non electronic chargers will charge a stone dead battery.
Thanks! I pulled the trigger on an new one the NOCO genius BOOST GB40. I keep it in my vehicle until open water then it goes in the Boat.
Have a Schumacher 1100 peak amp for the wife to carry back and forth to work in the winter. Just checked and its at full load even after sitting in the garage all summer. Got it at fleet Farm last fall. LB