I have replaced the battery with a new one, and still have the same problem, so at least in my case, recharging the battery wouldn't do it.
Also, regarding the last post about "magic reset", how would this differ from just removing the negative lead at the battery? I don't see how the car would know the difference, though I'll give it a try. My battery was already out of the car for a day, so I expect it would have had the same effect. I didn't see anything about the reset taking care of the nav and radio problems addressed in this thread, is that something from your own experience?
Thanks everyone for the advice, either way.
Ted