US 2002 Focus LX w/AC that I bought a year ago. Three or four weeks
ago I noticed that it was cranking somewhat slower than usual. The
next day or two I noticed the dash lights seemed dimmer and then the
radio started going off and on. All this time there were no warning
lights on the dash. I got it over to Checker where they checked the
battery and said it was dead. Replaced the battery, I charged it at
home for good measure and all seemed well.

Last week I started having problems again. This time I hooked a DVM
directly to the battery posts. The voltage while driving was all over
the place: 10.5, 12, 11, 9.5, 12.5, 8.5, you get the idea. On the
freeway the readings were generally on the higher end although never
higher than 13. In town and at idle toward the lower end until it died
as I pulled into my garage. Again there have been no warning lights. I
charged the battery again.

Definitely a charging problem of some sort. Alternator, regulator
or ??? Is the regulator in the alternator? I added the ??? since I
read somewhere that the computer actually handles the regulation.
Change the alternator myself $, take it to favorite local mechanic $$
or Ford dealer $$$. Decisions, decisions.