Voltage Regulator?

A friend has a ’96 60 hp Merc tiller. His starting battery keeps dying on him. I think it’s the voltage regulator, but I’m not sure. Any thoughts out there?

On his Lawrance 350, the voltage runs from 12 to 12.75v, once in a while it will hit 13 volts but very seldom. I’ve checked this with a vom and that’s about right. I think it should be putting our 12.75 to 13.5 or better.

New battery. Marine band radio, sonar, speed, tac ect all connected to the starter battery.

While the motor is running, we unhooked the ground from the battery, the motor ran fine.

I think there’s enough voltage to run the motor, but not charge the battery. Using an amp meter, it shows about 1.5 amps with the motor running.

What did I miss?

Was this just at idle, or across the RPM range?

On a car, voltage typically reads 13.5-15, I suspect that it’s not charging sufficiently.

That would be the whole range…from idle to wot. I aways thought that the voltage regulators either worked or didn’t work?

Sounds like the regulator to me as well.

At low RPM, the regulator doesn’t clamp because the generator/alternator isn’t putting out enough juice to require knocking down, so typically you’ll see it vary some when you run the revs up if everything is working.