[blue62]

If your going to test the alternator, test it at the alternator not the battery.

You could simply have a bad or dirty connection at the battery, ground points, or connections at the alternator or faulty, damaged wiring. If you want to test the alternator start at the alternator, if it tests good then do a voltage drop test at each wiring connection. Work you way to the battery.

If the alternator is in fact faulty replace it. Then do a voltage drop test at the battery cable connections. If you have voltage drop then find the bad connection or wiring by doing voltage drop tests on the wiring and wiring connections from the alternator to the battery.
If no voltage drop then charge the battery and have it load tested.
By testing this way the entire charging system is tested and proven good or faulty and the faults are found and corrected.

The way your testing you could conclude that the alternator is bad when it could just be a dirty or loose wiring connection. Spendy mistake.

You have a multi meter, go to youtube and watch how to test automotive charging systems, also how to do voltage drop tests. Or google testing automotive charging systems. Also how to perform voltage drop tests.