We have a 97 Bayliner with Mercruiser 5.7 engine and Bravo 2 outdrive. The dash guage only reads 13 V when fully underway. It also drops to 8 V when under 1200 rpm. I figure the guage is 20 years old and just doesn't read real accurately. The batter runs low if we cruise a lot under the 1200 rpm level. The question is this- Is this normal to only charge when over 1200 rpm? Is there an alternator swap or other change that would let it charge, at least some, at idle speed, more like a car?
