Lithium batteries in "conventional form factor" arrangements (as opposed to "power pack" type units), particularly the "non-smart" type do seem to be getting cheaper, imho?
I recently obtained from Sterling Power (whom I consider to be a reliable UK based dealer, and designers/manufacturers of electrical power products with a good long-term reputation) a 100 AH LIFEPO4 battery for £340. Obviously manufactured in China, as are many of their other products, but SP have been around for years, and are still something of a family firm; excellent to deal with. 5 year warrantee.
This will replace my 100AH ""Rolls" brand AGM lead acid house battery. No idea how old this is, but should still be OK for another season. However the peltier type "picnic box" fridge/heater really hammers it (also spoils your breakfast if you unwittingly press the red "heat" button, rather than the blue"chill" button!
LIFEPO4 only a little smaller, but approaching twice the useable power, at half the weight.
I didn't want want/need a Bluetooth battery monitoring system (I have a Victron BT mains supply/charger, and while the BT is interesting, it's a bit of unnecessary faff, imho). Note also that SPs Blue Tooth BMSs are not covered by the warranty...
I have a hard wired BMS, and a SP 12v 25A Battery-to-Battery charger that cross-couples the start (lead acid) and house batteries, charging the house (now Lithium) from the engine, and the starter (conventional Lead acid) from the solar if/when the power is available from each source. The Victron couples any shore mains to the Lithium, and is continuously rated at 15A.
Not sure that the above setup is appropriate for open boats, but should suit cabin boats?
Suspect any LIFE04 weight savings will be absorbed by the BMS, B2B charger and shore power charger (luckily all in the same relatively central, low down locker)! However, the master plan is that I won't need to so-closely manage Mrs SSs use of the fridge etc!
I'll keep you posted as to how it goes...
What does Swallow fit to a 26 these days?