Alternator?!?!?

[Centrevillemx]

I think I may have a bad Alternator. I charge the battery to about 13 volts run it for 1/2 hour and the voltage drops to 9v. I cleaned the contact points on the battery and it did it again.
What do you guys think??

[Ghost]

You have a Advanced Auto up there? If so they can test it on the Jeep in the parking lot for free.

[Centrevillemx]

We have a western auto, but the jeep failed emmissions and it doesen't have tags.....

[andyr354]

Make shure the alternator is getting excited :)
One way to see if an alternator is charging is to test for magnetism. When it is charging a wrench will stick to the back of it.
If it is not first check the exciter wire. In that two wire plug on the alternator both should have power. If they do, and the alt is not charging, it is most likely bad.

[juicexj24]

If it failed emissions than the O2 sensor is bad, or EGR valve. Just take the alternator off and have a parts store test it out. I did that with mine. Juice

[Centrevillemx]

juice, i'll try that "taking it out and taking it to the store" thing :)