One of 2 possibilities. Either the alternator field is being shorted to voltage causing full charge output. Or the regulator field output is high because the regulator is being tricked into thinking alternator current output is low. Since you just replaced the battery I'd be looking at those cables first. Voltage drop test from negative battery post to reg case and alternator case. Voltage drop test from battery positive post to reg ignition feed, alternator ignition feed, and alternator output. Voltage drop regulator field control to alternator. Do all these while running under load. You'll find it.
Doug