Our local Autozone(and Advance, and Pep Boys) all have alternator testing machines that will spin and test an alternator outside of a running vehicle.

I'm not sure how good/accurate it is, but it'll tell you something.

-John

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2009 Kia Sedona
2009 Honda Odyssey EX-L
12006 Jetta Pumpe Duse
(insert Mercedes here)

Husband, Father, sometimes friend =)