I did a ton of learning and talked to a lot of people like you and at battleborn batteries. In the end this is what I ended up with for alternator charging a lithium battleborn battery in a Ram Promaster van.I ran a 4 gauge wire to a high quality 70 amp auto-reset breaker, then to the cyrix li-ct, then to the 100 ah battery. I used a small piece of 16 gauge wire to connect the bms terminal on the cyrix to one of the large terminal posts on the cyrix. The battleborns have an internal bms so there's no need to have an additional bms. As long as there is any voltage in the battery post you're connected to, it will keep the cyrix 'awake.' That's all that post does. You could also wire it to an ignition-activated wire to ensure that it isolates when the vehicle is off immediately, but that is unnecessary.The cyrix does the job. It connects the batteries when either one is above 13.7 volts. So if you plug in 120v to the inverter/charger, it connects the batteries and you run current to the starter battery too. Same for starting the engine, it connects the batteries above 13.7. Once charging stops, the batteries stay connected until the lithium battery drops to 13.5 volts. Resting state for a fully charged lithium is right around 13.4 so this works great. So everything is good except one thing:A drained lithium battery will take just about any amount of current you can throw at it. The test I ran was to drain the battery to 40% capacity. About 12.6 volts. I started the engine and immediately got a 65 amp surge, then it settled at 55 amps. The wire, breakers, cyrix, etc can handle that big load, it's the alternator I worry about. I don't think many people think about the alternator when building an alternator charging system with 150 amp breakers and 0 gauge wire. Even at 65 amps, you can hear the engine idling low and the alternator working really hard. For extended periods of time, this would wear it out and at higher loads could cause malfunction in the vehicle itself.So my theory is that with a 100 ah lithium battery, this system is great. Up to 150 ah system...borderline. I bet repeating the same experiment I did, you'd see a 100 amp surge. Promasters have a 180 amp alternator so it can probably handle it. A 220 amp alternator would be better. But I think if you move up to a 200 ah system (or bigger) it's time to get a dc/dc charger that will limit the current to 25, 40, or 60 amps depending. The next van I'm building, I'm putting in 200 ah lithium bank and using a 25 amp Redarc charger. I got it in the shop and it's a really nice product. Very small, sealed with inputs for alternator and solar (mppt) charging. They also make a 40 amp version and just released a 30 amp unit that has inputs for alternator, solar, and shore power (the unicorn of charging devices!) It comes with a battery monitor and costs $1200 which is a bit crazy even though it looks like a great device.
This is on a 50 ft Catamaran. The batteries use the Elite Power Solutions BMS and 1100Ah GBS LFMP batteries. There are five charging sources 1) shore power via the Victrons, 2) genset via the Victrons, 3) 1040W solar, and 4 & 5) two engines each with Balmar AT200s, MC614s and a Centerfielder.