How were the battery and alternator tested? Were they tested in the car using an instrument that just touches the positive and negative terminals? The kind that AutoZone will do for free? In my experience, these are not thorough tests of these components.

The alternator should be removed and placed on a testing machine which will spin it up to speed and measure not only volts, but more importantly amperage output. Similarly, a dedicated battery load tester will provide a more accurate test of your battery by simulating a deep discharge. I believe Autozone may perform these tests, but I'm not sure. Old-school type parts places which *tend* to have more knowledge will definitely do these. Napa and some local CarQuest places come to mind, depending on where you're located.

In my opinion, the in-the-car tests are just for rough overview but aren't very thorough. It's similar to the handheld code scanners which just give you a rough guide to start troubleshooting but don't really tell the whole picture.

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