The problem to my mind is that the solar panel keeps putting out its power indefinitely while the battery capacity is finite. That is why I used an extimated per day self-discharge as my basis for picking charge capacity that would maintain the battery. Incidentally, I assumed 100% charging efficiency which is hardly he case. I have seen numbers ranging from 70 to 90% charging efficiency. However that number depends on the state of charge, age and temperature of the battery. I did find one paper from Sandia Lab that concluded that above 80% charge lead=acid battery charging efficiency from a small solar panel is as low as 55%. Thus, you can probably get away with about 1 watt of rated solar panel output per 100 amp-hours of rated battery capacity for an over wintering system where the batteries start out close to full charge. This number app;lies to a fixed panel here on the Maine coast and not to anywhere else.

Actually, the 1.5% number for an unregulated solar panel is probably just fine in the summer when the self discharge rate is much higher than in the winter