charging issues

I have a 2019 se 550.
5 alternators ,2 new harnesses a new main screen and a loose ground wire. Had to take it to out of state marinas during 2 vacations. ugh.
got it back Friday and ran it yesterday. volts are still bouncing 14 to 13. this is how it starts. sometimes it would not go above 12 volts. I shut it down and start it up and it starts charging. all videos I watch online the volts stay at 14 when the boat is running. I know the dealership is trying but they can't solve the problems. does anyones supra have volt issues?