Hello Scott (and others), sorry to keep adding to this original thread but I thought I might share my experience converting to Lithium and Victron Multiplus inverters. I know there have been many discussions round this topic, so hopefully Amelians out there who are considering this plunge will be able to do it based on others (and my own) successes and mistakes.
On my 54, I installed 12 Battle Born 24V batteries to replace my Fireflys. I installed the Fireflys after my previous AGMs exploded. Unfortunately, the Fireflys essentially gave up after about 3 or so years. I just could not keep the voltage up, and ended up with a lot of low-voltage problems, most likely because of the fact that you have to series 2 of them and then parallel the 6 pairs to get 24 volts. I suspect their early demise was because I did not balance the series pairs.
With the new Battle Borns at 24V each, the series issue is gone and the batteries consistently hold more than 26 volts under any conceivable load state. The new batteries are much lighter than the AGMs, which is a bit of a problem, as now I have a slight list to port - not too noticeable really but still not ideal. Anyway, the install went very well and I am happy the voltage never drops now even as you discharge to more than 50%. With the AGMs, my Maretron alarms would wake me up in the middle of the night until I started the generator to get the voltage back over 24 volts. The lithiums also accept full current from my chargers right up until they get to 100% (I can now charge with 70 x 2 or 140 amps). Again with the AGMS and my original Dolphin 100A and 30A chargers, the current acceptance would ramp down big time after the batteries reached about 80% charge.
I also installed dual Victron Multiplus Inverter/Chargers (3-kVA each), eliminating both Dolphin chargers. I use 1 of them as a battery-charger "only" to avoid having to run new cables to the batteries - if I used the inverter function, I would have needed to run new monster DC cables. As installed, I was able to use the original Dolphin cables for the charger-only Multiplus. The second Multiplus replaced a similar Victron inverter-only unit I installed a few years ago. Since I already had run fat cables for the inverter (yes, as Scott noted, you have to bust out the epoxy seal between the engine room and battery compartment - I plan to reseal shortly once I have all systems proven), I was able to use it as an inverter and charger as designed. That gives me 3000 VA for AC loads, which seems to be just right for my needs. I split the AC panel in half, feeding one side with "normal" shore/generator power, and the other side with either inverter feed or shore/gen power. I used a simple Blue Sea selector switch to do that. I also have essentially a "spare" 3-kVA inverter if I need it in the future. By the way, I retained the Amel systems right up to the main AC breaker at the AC panel. I ruled out feeding shore power through an inverter/charger (which is common approach), as that would preclude the ability to run appliances at 50 Hz while simultaneously using 60-Hz shore power in the US.
The only issue I see now with the lithiums and charging is that the batteries tend to heat up a bit with a really large DC current. I throttled back one of the chargers a bit (using the Victron Connect system) to allow more "gentle" charging. I use the reduced-output Multiplus when I just want to do a slow charge, and both for fast charging. Changing the DC output is quick and easy, although I wish Victron would allow me to do it via bluetooth on my PC. Right now they only support phones and iPads.
The inverter capable "bus" side of the AC panel allows me to run the fore or aft air conditioning, the dishwasher, washer, dryer, microwave, and AC outlets without shore power OR generator - although not all at once!! I have tested all of these functions and found one issue - the AC power for the Climma relay box (which powers the AC pump) was fed from the non-inverter-capable side. After some head-scratching I decided to move the Climma panel feed from the other "bus" to the inverter-capable side. Until I relocated the feeder, the aft/foreward AC units never turned on the pump, as it was fed from the "normal" power side. Those who might use a quattro or larger inverter might not have this problem if you decide to feed ALL AC breakers from an inverter.
I still need to replace the Mastervolt alternator regulator, and I have one on order right now. The new regulator supports lithiums, even though some modifications may be needed to shut down the regulator when the batteries are full. I may need to do that manually, as the Battle Borns do not talk to the Victron BMS. That is a project I will attack shortly.
Although not as "exotic" as Scott's system, I am delighted with the new setup as it works for my needs, and would be happy to share what I did in more detail if anyone is interested.
Phantom, A54 #44