Are you sure it was working right before? That's probably why you had to replace the battery...
SR
Out put voltage at B+ terminal of alternate when proper charging should be 14 volts (+/- 0.2 volts).... IF not alternator has a problem... If there is a regulator associated with alternator it could possibly be problem...
Also check if system has a ALT lamp. some systems require a shot of 12 volts through ALT lamp to initialize charging, if lamp is burnt out it may effect how alternator operates....