Bored, can’t sleep. Just looked up prices of Lithium batteries, GC2. The cheapest I saw was over $2,000 per batterie. So I would be looking at about $10,000 for my house bank of 4 GC2 batteries? Really? What am I doing wrong?
I'm not sure where you are looking, but there is hardly a typical group size on the site linked below that is near that price level. Not many sailboats use 8Ds. Maybe your battery size is the unusual variable and there is a near match that is more affordable.
I currently have 4x Group 31 Gel batteries at approx 100ah each, which cost approx $475 each. That was a total of $1,900 for 200ah of usable capacity (50% of total capacity).
If I were to upgrade to lithium, the attached shows Group 31 lithiumPO batteries at $1,050 each and the same 100ah total capacity in each. However, you can run a LifePO battery down to 20% SOC, so that's 100x4x80% or 320ah of usable capacity for $4,200.
At least for this brand, lithium is twice the cost, but one gets 50% more usable capacity, superior charging profile (ie much less generator/engine time or faster renewable charging) and they weigh about a third of what the Gels weigh.
It would be cheaper to add even more weight and batteries, but for those who are space or weight constrained or value the faster charge rate, lithium has value.