All lithium batteries put a big load on alternators because the batteries have a very low internal resistance. What that means is that the alternator will run flat out much of the time. In addition this 120 Amp model Cyrix might be too small if your alternator can produce more than 120 amps.
There are a couple of other ways of doing this. One involves using the new Victron BMS which allows you to modify how much power is taken from the house system. The other way around this is by using a DC DC Charger to limit the current flow.