Thanks so much everyone for telling me how your HCH's run, very helpful. The trick with the headlights is very good to know.

I did get a loaner today, after talking to General Manager. Oddly enough, no one is able or willing to give me the name or number of a "regional" manager, just the dealership manager or American Honda. But I will keep pursuing that. Right now the dealer is trying to help, but they still can't figure it out.

Things I have learned:
If a Honda factory tech tells a local dealer's service tech that the car is running within acceptable specs, the local tech is bound by that, so I would have to take up the issue with the factory.

Honda is still not getting my point that whatever specs may say about how a HCH can run fine as long as the battery has some charge, and that it is normal to have a half charge or lower--that this particular car, my car, has suddenly changed. For 25000 miles it runs with a nearly fully charged battery and then one day it breaks down and now it runs at half battery or less ... to me that would be a good place to start in trying to figure out why it broke down.

Coyote, good point about the internet. I had thought of the google aspect, because I found this forum through google myself.

Right now I'm waiting to see if they come up with anything while I have the loaner because I am going to be really busy for a few days and just grateful to have a plain ordinary Civic as a loaner. But I really don't expect them to diagnose it. They keep saying they need for the codes to recur and for it to exhibit the error lights and failure to run while on their watch, and the car is stubbornly running OK (except for the lower battery) whenever I take it in.

Oh, and I don't know my MPG. I always run the air con so I don't think it's that great.

Also, I never use the auto-stop function, so I don't put that strain on the battery. It is much too hot here to sit at intersections with the windows up and the air con off just in order to save gas by not idling, and if I rolled my windows down I would have to re-cool my car (and be hot)--so I think the auto-stop is just not a real payoff in my climate. (Hawaii, Big Island, Hilo).