I had been hearing an old-belt-noise from my wife's car, kind of like a whirring chirping noise. I was going to do the repair the week between Christmas and New Year.
Get in the car Christmas Day to go to my relatives, driving down the road, and sure enough I see the radio display blinking on and off, which is an indicator that the battery died. I get to my destination, turn the key off, then try to start it and it was as dead as a door nail. Hooked up a trickle charger, and left it there the whole time. Got in it to leave, and it started.
Got up today, did a volt meter test on the battery at rest (low volts, 12.03) and with the car running (also low, 13.1). Good numbers for my vehicle would be 12.7 and 14-15, respectively. Also, with the hood open and engine warmed up, the noise is obvious. Bad bearing in the alternator. I'm showing my age saying this, but it sounds just like if you held one of the keys down on an electric typewriter. Or a low-volume sewing machine. It's also intermittent. You won't hear it when it's first started, but go a few minutes and then it kicks in.
I called the local auto parts store this morning, and I should have an alternator at the counter late this afternoon or tomorrow (pretty good for day after Christmas).