There’s more than one way to configure it, but for the most part it’s a parallel scenario, and often* necessary to protect the alternator when using LiFePo4 batteries - Why?? Because of (if one dare believe Victron, et al...) LFP’s high current receptivity...Also, for newer vehicles, the dc to dc converter needs to be ‘Smart Alternator’ or Euro 5&6 compatible...
*depending on components and load
Here’s an interesting primer on the subject:
https://www.youtube.com/watch?v=dzU_pQFa19s&feature=youtu.be
3 tons