battery charging problem

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.
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azjerry wrote:

The regulation is handled by the ECU.
Before replacing the alternator, check and recheck all connections relating to the alternator, and all under-bonnet earths. (Not sure of US terminology - sorry!)
It could be alternator brushes, but I would make sure that all connections are 100% before shelling out for an alternator that might not be needed.
HTH
Chris
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Chris Whelan wrote:

Usually referred to as ground over here.
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me wrote:

Ah, OK - thanks.
Two Nations separated by a common language, eh?
Chris
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