Got somebody to jump it off without electrocuting either of us, made it home, and next day, same deal. Battery was nearly dead.
There are several things that can cause this: Alternator, voltage regulator, a short in the electrical system, or a bad battery. Given that the car is nine years old and still wearing the original factory-installed battery, that was my first thought. Generally, after five or six years, the batteries give up the ghost, usually on a cold day.
My mechanical abilities are slim, but I can pull a battery out where it is accessible. Never seem to have exactly the right tools, but that's why God made Crescent wrenches and pliers, and I managed to get the old one out, drive in the wife's car to Les Schwab's and swap the dead one for a new one.
Cannot believe what those suckers cost these days, but it's been like fourteen years since I bought one, and this was the top-of-the-line Extremo Mondo Whatevero model, good for seven years, yadda, yadda. Came home installed it, car cranked right up, and, I hope, problem solved ...