New battery should be around 12.5 volts, however you
have been playing around with it some. Your Battery sounds OK.
Could be the starter but you want to do the free stuff first.
Disconnect the battery and clean all the connections in
the system well. That would include the battery cable
connection’s as well if you haven’t done them already.
Could be just a dirty connection and the starter isn’t
getting all 12 volts.
Tubs
A "Boathouse Repair" is one thats done without having tools or the skills to do it properly.