Alternator - how do you know if it's faulty?

[cwiert]

The battery in my car wouldn't hold a charge if it wasn't driven for a week or so. I'm chalking that up to a bad/old battery, so I replaced it.
I have one of these "smart battery chargers" that has an "alternator check" on it. I did a no load check (no accessories on) and it passed. Then I did a "load" check (turned on the radio, the lights, the fan) and it failed. I tried to single out what was causing the failure and found that any accessory caused the failure. The book with the charger says a "load failure" can mean a faulty alternator, bad ground or other connections between the alt and battery.
But I did my own old school, 5 second alt check which involved starting the car with the lights on and then turning the car off and seeing if the lights dimmed. and they did. since the battery is 12 volts, and the alt sends out 14 volts, the lights are a little brighter with a working alternator on a running car. so that checked out ok.
basically, i'm just wondering if this "alternator check" failure on the battery charger is something that should concern me.
thanks.

[Grandad#3]

If you are worried about the alternator drive, the car to Auto Zone or Advance Auto and they will check for free.

Cheers,
Larry

[Icey1174]

Autozone just checked mine, it's bad. It was all over the place. It was putting out 12V one second then down the 7V up to 8V, back down, all over the place. I know what I will be doing very soon.