Get another battery, I know Napa has high end battery analyzers that take a minute or so to thoroughly test a battery. I had an older battery in our Class A that had been performing well during three days of a week long excursion. Had very similar symptoms after stopping at a Loves to get propane, took it to Napa and had it analyzed. It was shorted showing only 4 volts, they have most any battery size and we were quickly back on the road. They employees at Loves tried to jump it and according to their equipment all was fine, they suggested having it towed.