My boat is a 1996 Maxum 2300SC with Mercruiser MCM 454 Bravo 1 Gen V 1996, serial 0f362346. My batteries had died from leaving a light on in the cabin, I jumped the boat in the drie, ran it for 20 min and headed to the lake, boat started up fine but then died the next morning on the lake. I got a jump start and headed home, I noticed my volateg meter was running at 11 olts at 3400 rpm. I got home and double checked with a meter and yup, 11 volts at 2500 rpm. I charged both the batteries, both read 12.6V and crank nice, the voltmeter is still reading the same.. Took the alt out and took it to a reputable starter/alt shop and they tested it, said it was fine. Came home, installed it back in the boat, made sure the belt was tight and same thing is happening. at idle i get about 12.5-13 volts, once rpm ramps up it drops down to 11.5-12 volts. Any ideas? Is the alternator crap? They tested it with the regulator? The shop blamed it on a little bit rusty pulley and loose belt.
