Sounds like the lead batteries definitely help the list problem!
Good analysis, and I tend to agree about it being marginal for part-time cruising. I have a good solar capability, and I'm sure I would get 5 years easily from some good AGM batteries.
I don't anticipate a big drop in Generator usage by changing to Lithium, and I like to run it for a reasonable time on a regular basis anyway just for good practice.
It looks like I'm getting close to an answer on the cost comparison on a drop-in replacement basis.
Its about GBP300 for a new Alpha Series III regulator, and another GBP200 for a USB interface to program the chargers, so that brings the Lithium package to about GBP8500 vs around GBP3000 or maybe a bit less for those Leoch Carbon AGM batteries.
So I save a heap of cash and don't list even more to port by sticking with the lead! Who knows what new toys I could buy with that GBP5500.
Very interesting exercise, I need to mull over this a little more.
SY Stella A54-154