Mark I know youíre a Li fan still many arenít. Take a peak at affordable cruising or look at whatís inside most cruising boats. It isnít Li. Iím on year 6 of my lifelines. Probably put carbon in when they go. Space and weight arenít a concern. With solar and wind getting to 100% soc isnít as well. Cost is. Replacing/ reprogramming charging systems is.
At present with 1020 usable amp hours isnít. Getting to run the generator with a load is.
My situation is not unusual so Li is overkill for many.
OP asked a good question. Iíve been told for a full time cruiser 8-10 years is reasonable. Thatís a passed along opinion. Take it as such.
I'm not sure why you are addressing this to me. I'm happy with whatever battery people want on their boats. As far as my posts on LFP, I was only addressing some misconceptions, and warning people about "experts" who may not actually have any real experience with them. Same for the carbon foam above.
You will pay the same for Firefly as for LFP. Programming charging sources should not be onerous. Replacing poor charging sources could be - but these types should probably be replaced for the sake of any battery chemistry health. Poor charging sources kill lead as fast as they do lithium. I can't think of a decent model of charging source - solar, wind, mains - that can't safely charge lithium. I can think of bad models that can't, and shouldn't be used with lead either.
8-10 years for a battery bank for a full-time cruiser is optimistic. That is from real experience over this time period with optimized charging, electrical, and battery maintenance systems. Gel possibly, FLA not.
As I understand it, your bank is not in use full-time, so 6yrs is not a full-use lifespan. This is not a judgement, but it is important to note. Some here have been describing the life of their battery banks, while discounting the fact that the banks are laid up half the year, and hooked to the dock doing no cycles, or shallow cycles, most of the time when they are in use. Many more years of life should be expected for these batteries over heavily used batteries of the same type - but one cannot make lifespan claims in general without noting this important point.
Most people who are heavy use and think they are getting long lifespan have over-provisioned, and not realized until the end how bad their batteries had become.