I'm kinda new at this but I learn fast, I have a bit of mechanical knowledge but, by far I am not a mechanic.

1. I have had some battery issues
Replaced battery to much larger marine deep-cycle/starting x 2 and they started the boat no problem but drain after operation.

I took off connections and cleaned them at the altenator + Added some di-electric grease and noticed a black (ground wire?) was loose. I have re-connected it and am waiting to trickle my batteries before I can see if it works. I don't have a volt meter so I am just running it for a while to see I if it will work.

If the Altenator is shot, how hard is it to replace?