What you need to do is put a voltmeter on it and see what it's putting out for voltage at rated speed... and check it again in 10 min, 30, min 60 min and see what it's doing then... with the engine running at mid speed or more. If a battery is low it will take time for the voltage to build up. Once it reaches charge then it will climb until it boils...
You've got 14.4V so you know the gen is working fine. What you don't know is wether or not the regulator is A. limiting current, B. Limiting maximum voltage or C. wether or not the cutout is working.
I'd be inclined to suspect that the cutout is simply not working on the reg... contacts welded shut, etc.
It could also be a wiring problem that is not allowing the reg to correctly sense the charge voltage..
First step is to accurately find out what voltage is reaching the battery over a period of time... then you know where to start looking.