Duracell Batteries
I think 1st you should decide or review 2 things.
1st, how do you plan to use the boat in respect to battery use? 2 of any battery might not be enough so the type of battery isn't at this point important.
2nd, how are you going to charge your batts? Do you want to use the generator or are you going to charge the batts off of your engine(s)?
Thinking of your intended use of the boat is important. Are you going to be doing mostly cruising for long periods of time or weekend jaunts? Long runs or short?
Are you planning on anchoring out extensively or just occasionally?
Do you have the ability to put more batts on your boat, weight & size of a location is important?
With usage questions answered, you can plan on batts from there, but batts are only part of the equation. How you will charge them is a bigger part of the equation.
Providing power for a boat is a large investment (maybe I should say an expense) but to get your boat to a point where you can leave the dock, go for a couple of hours and stay a couple of days on the hook takes heavy deep cell batts.
I'm not going to answer your questions until I have more info, answers to the questions above and then I can offer some advice to help you accomplish what your goals are.
I will offer this. Go online and find an energy usage estimator sheet. This will help you see, other than a refrigerator, what power you use and what size batt bank you need to meet your needs.
We have 6-L16 AGM batts. We can stay on the hook, running our refrigerator the whole time, make coffee, cook dinner, basically live a normal life for 2+ days without recharging (we don't have a built-in generator).
Send me a private message and we can start a conversation.
Good luck in your pursuit.