I don't know what system Thor uses in the Plazzo but it sounds like you have a bad BCC (Battery Control Center). In the Axis the BIRD (Bi- Directional Relay) does the same things but in your large coach, you probably have a BCC or something similar which allows the engine to charge the coach batteries and shore power/generator to charge the chassis battery and disconnects them when the coach is not on shore power/generator and the engine is not running. Thor will be able to tell you what system in in your coach performs these functions.
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