No - but thanks to Ultra Willie, I'm working off a new theory. He strongly suspected the alternator, which I doubted that at first. After thinking about it more, here's an alternator scenario that I'll be able to test tomorrow.
Last summer, if the alternator was starting to fail, the battery needed more and more charging before we'd go out every time. Then a few weeks ago when I put the new battery in and charged it for a while, we were able to drive around with no problems, but it pretty well drained the battery. Ultra Willie suspects that a few days later when I went to turn on the blower and radio, the battery was too drained to do anything - even get LED lights to pop on. (He had an interesting battery theory about needing a minimum amount of juice for a battery to do anything - in other words, the battery won't discharge energy in a linear way. There is some threshold where the battery goes from functioning somewhat normally, to not at all. Some kind of protection mechanism
After quite a lot of charging, now all the electrical things work normally again. Measured 12.25v across the battery terminal and that seems pretty normal.
Tomorrow I'll have a chance to dump it in the water and test while running. I believe I'm supposed to get 1.5v to 2v higher than battery voltage at idle. Is that correct? Does anything less indicated a bad alternator? Is the voltage regulator connected to the alternator?