My four year old batteries were not coming up to charge, I would see the
voltmeter reading 13 volts. I tested the alt. at idle, and at about 1500rpms. I
took out the batteries and had them loaded, the verdict was to replace them
(which I did). The problem is at idle everything seems to be great, but at
higher rpms the batteries discharge, I see a steady discharge on both the
voltmeter and the digital display on my sonar. How do I determine if its the
alt. or the regulator. The motor is a 1999 4.3 ltr mercruser and has the 55amp
mando alt. Thanks for listening.

John