Thanks for your comments Turnerfam. MB confirmed that there is no "Emergency" switch to engage the house batteries to boost the chassis battery. With the key removed and the "use/store" switch in store, nothing is apparently on. RE disconnecting the negative lead from the chassis battery, on our coach it's under a panel in the cabin in front of the driver's seat, so not easy to routinely access. Will poke around further, thanks again...
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