Originally Posted by Nos4r2
It won't be your battery in any case. The alternator on that motor is old tech and it doesn't have a massive output. Certainly nowhere near enough to overwhelm a battery the size of the one you have.
Having kind of a similar issue on my Yam 90 AETOL. When battery is fully loaded and the system does not have any power consumtion, voltage goes very high, 15V-15,5 V. But if connecting the running light(40W) or if batter is not fully cherged, figures are normal like 14,3 V.
So this is not then battery related(60AH, slightly less than recomended), would it be a faulty regulator/ recitifier, not an issue to worry about or maybe a faulty/loose isolator swich?