When your battery is not being charged by the alternator the output can be tested

If you are not sure if the regulator or the alternator is defective you can manually put a voltage of the field wire and see if the output goes up and starts charging the battery.

Increasing the Field voltage should increase the alternator output

Alternator is outputting 80 amps

Balmar makes an inexpensive constant voltage regulator that can plug into their existing cable harness. The alternator output voltage can be set using the small screw on the back.  This can be carried on board as an inexpensive backup.   

Alternators can be bench tested to verify their max output.