I have a single series 31 for starting both engines.
I have two series 27 Duracell deep cycle for the house.
People have argued with me, they are not deep cycle, but this is how they are advertised.
https://www.samsclub.com/p/duracell-marine-battery-group-size-27dc/prod3590231
One group 24 to start the gen repurposed from a car.
Honestly so far, have no need for a huge battery bank.
I do have a generator of 6500 watts.
My idea is get by with minimal batteries because they all go bad.
When they show signs of issues, I replace them. I use them up. No one would want my old batteries. Rather than sulphating they seem to develop shorted cells, but maybe because they sulphate, they do that.
I still get anywhere from 6 - 8 years of use regardless of battery price or quality, except for one 8D I bought which internally shorted out in under 3 years. Huge heavy piece of junk, hurt going in, hurt while using it , hurt coming out. Then it hurt hanging around the house for a few years, and hurt taking it back in to recycle it for $20 cash.