I suspect that a lot of us are looking at the same question as our AGM batteries get to the end of their life cycle.
AGM vs Lithium: Because the (2) 75 Ah AGM batteries (standard in FWC dual battery set ups) can only be drained to about 50%, a single 100 AH LiFePO4 battery, which can be drained 90 plus percent, can provide a similar number of Amp hours. The initial cost of Li is higher, but the lifespan (because it can go through more charge cycles) promises to make the initial cost a break even by lasting longer.
Protect Your Alternator: What I did not understand was that a Li battery will draw more to charge than your AGMs. This is because Li batteries charge faster. Most truck alternators are not built to handle that extra work. Now, if you have a 3500 with a big ole alternator, you may be okay. Otherwise, you need to protect your alternator from overworking -> overheating -> letting you down : (
The DC to DC charger is made to protect your alternator by throttling down that charge. By limiting the amperage on the charge side, it protects your alternator from overworking and getting you in trouble.
Now, full disclosure: I'm learning about all of this as I prepare to change over and let my 5 year old AGM go. All of you much smarter folks should feel free to correct / redirect / teach me / us : )
My plan is to use a DC to DC Charger (Victron Orion DC to DC 12 / 12 / 18 Amp) and a Battle Borne 100 Ah LiFePO4 battery. https://cemarine.com...ly-ori121222120
Any hints, suggestions, etc would be welcome!