Expert: Everett Peacock - 11/14/2011

Question
I have 2 new batteries on my boat.  I have a 2000 Yamaha F100 motor.  When I go to use my boat, the batteries are usually dead.  I have a built in charger so I plug the charger in and the batteries charge right up.  I am getting 12.5 volts when the engine is on, but apparently, the motor is not charging the batteries because when I come back after running the boat for an hour or so, the batteries will not start the boat.  How can I check to see if the magneto is putting out enough juice?  I'm also thinking that I may have a bad connection somewhere.

Answer
12.5. Volts are not enough.  It should be at least 13 when running..it more than likely has a rectifier or voltage regulator..it gets it's voltage from the stator which gives out a  ac voltage, the rectifier/voltage regulator converts the ac volts to a usable dc voltage...to charge the batteries...