Electrical Help Please

#3 and I'd love for someone to help me understand the capabilities of the BCC when my book says while on shore power once the house batteries get to 13.3V the relay opens and sends current to the chassis battery and just the opposite when the engine in turning the altenator. Either they sent the wrong book with the coach or the BCC has been switched out. It's 13 years old and we have had it for 2 weeks so it has a history before us but the previous owners said the shorepower charges both house and chassis. I've googled and found nothing and was just trying to find an answer here.