Nuevo ES 2022 Flat Vehicle Battery

The heavy current is on charging on these vans. 
My 2001 Hymer was fitted with the Electroblok 99 charger and I never knew how the charging arrangements were wired. However there were two 50A fuses, one close to the vehicle battery and the other near the leisure battery under the passenger seat. If the vehicle battery became discharged and you tried to start the engine unaware of the low battery one of those 50A fuses would blow. It gave the impression that the starter was trying to take its current from the leisure battery! The first time it happened I was unaware that the fuse had blown and wondered why my leisure battery was flat after 3 days of holiday!