2003 Yamaha F150 4-Stroke Alternator question

[authoritay]

I've got a 2003 Yamaha F-150 4-Stroke on a Triumph 191 FS. My battery died on it the other week and I had to use another battery (friend's spare) to start it. After starting the motor, I disconnected the spare battery and the engine died. I restarted the motor with the spare battery and got it back to dock. Disconnected the spare battery and it died again. The battery itself was dead and, come to find out, needs to be replaced. I connected a new battery to the motor, started it, dosconnected the new battery and the motor dies immediately as it did before. I've checked the fuses which are all in good shape. All the wires appear to be in good condition with no damage to the insulation or connections. I am left to believe that the issue is likely the motor alternator. If anyone has had the same problem, I'm all ears as to what you did to fix it.

[Sylvan 75]

Put a good battery in it and check the voltage now start the engine and check the voltage again if the voltage is the same or less you are not charging check back to regulator