I have two very beautiful 100 amp lithium batteries that are currently charging off a smart relay from the engine alternator. There is a battery monitoring system that van dad can access via an app on his very smart phone. It not only tells him the battery status and the amount of charge but also the amount of withdraw. So far, the van parents are running the refrigerator, the max air fans, and the lights, all on 12 volt. These barely put a dent in my battery capabilities. There will be many more additions to this remarkable power system. Stay tuned.