On more than just on forum, I got the distinct impression that the Ford Focus had some sort of mystery surrounding my Battery light symptom. At least four instances were cited where the post indicated both battery and alternator replacement did not resolve their battery light issues. $120 for a battery, $600-800 I read were typical costs for alternator replacements, all to no avail. From this, I concluded that there was some other potential cause for my problem.
I ended up buying a new battery, based on the results of a test by a local shop. Not the answer. I decided to put the old battery back in and drive the car till something fell out of it. Then, I would be certain of the defective component.
My alternator toasted on Saturday night. As I might expect, once the alt finally gave up the ghost, the appropriate computer shut off all non-essential electricals, providing all available power to the engine (and, I supposed fuel pump) until the battery was too exhausted. It got me as far as I needed to go.
In NJ, one of the few service agents open on Sunday was Pep Boys. They secured an alternator from NAPA and installed it in a couple hours for $472. No mystery, no rocket science.
Seems like my ST and I are back in Focus.
Now, onto the reverse light switch.
(The hidden message here-don't overcomplicate this. The way my alternator failed-lots of strange electrical issues. The grand finale-all electricals shut down until the battery was dead.)
I'd replace the alternator. If you're not confident doing it yourself-I wouldn't hesitate to take it to Pep Boys (as silly as that sounds). From what I've read-they gave me a solid price.