While out at FR Berkshire Diesel Division recently, I had a chance to talk with the technician who installs, and is expert on all the electrical systems.
He stated that while the MH is being driven, the chassis batteries are charged first, then when they are done, the house batteries are charged. While parked, the situation is reversed. If the switch on the console for altrernate startup (from house batteries) is held down, the situation is reversed.
Remember that when hooked up to shore power to recharge or trickle charge the house batteries, you must have both the battery disconnect switch (located near the floor next to the entrance door) and the house batteries isolation switch (in the compartment with the four house batteries) in the "on" position. The inside switch isolates most of the coach systems from the batteries, and the outside switch isolates the house batteries from everything external to the batteries, including the Magnum charging system.
Also remember that when on extended trickle charging (I'm hooked up to shore power year round, when not away on a trip), you are making hydrogen in the batteries, so you need to add distilled water up to the bottom of the fill rings in the batteries periodically.