shore power and battery charging

I'm a noobie to boating FYI. Just purchased a used Sundancer 300 and drove it to Port Washington, NY from Patchogue, NY with no incident. Took it out a few days later with no incident. Docked the boat, plugged into shore power and left the boat on shore power overnight. Came back next morning...

There are so many posts and articles on battery configurations that now I'm more confused than ever. I have a 2014 Sundancer 280 and am looking to this group for advice on battery configuration. There are two batteries. I bought the boat recently and the current set up is a deep cycle on #2...