Can you help me diagnose electrical problem?

[ReeseBobby]

Hello,

A week ago I found my truck wouldn't turn over in the morning. I replaced the battery, and the next day the same thing happened. Here is what I've done so far to diagnose. I think its the alternator, but would like some second opinions.

-Battery alone sits around 12V.

-When I connect the battery cables, the charge immediately drops to 9.5 or so.

-I pulled each fuse individually and nothing changed.

-I removed the alternator wires from the alternator, and the voltage drop stops.

-I jump started the truck, and at about a 1500 rpm idle, the battery charged up to 13.5, so the alternator started to charge the battery. However, at lower idles, the battery drops back down to 9.5v.

-I took the positive cable off the battery with the truck running. The truck ran for about 15 minutes, but the lights and such got dimmer until the truck finally died.

Are these all classic alternator problems? Is there a definitive test I can do at home?

Thanks a ton for your advice.