I have a 150 hp 4 stroke merc. its 2013. I had a deep cycle batter I have hooked to it and a bunch of electronics. Few weeks ago I charged it up and went fishing. Just the other day I noticed a fizzing sound. It was gas in the deep cycle. Today I pulled boat from garage and turned it on with the house connected, watching my lowrance units to see if the volts went above 14.7 to see if the alternator was what caused the other battery to build up gas and over charge ( at the moment i am thinking it was the Ctek charger). When I started the motor and pushed the throttle forward more to see if the volts would go up past 14.7 the motor shook like crazy, this happened earlier this year and I found an electrical connection had come undone, did it back up and it worked fine. So now i am trying to figure out what is causing it, this time the motor WILL NOT trim up or down while the throttle is pushed forward and shakes like crazy and starts to putter.... does that sound like alternator or something else? If I can figure out how to upload a .MOV file I can show it.