That doesn’t sound a lot of good then. If both batteries are down to that level or possibly lower for the start battery then not much hope of starting the engine I guess. I wonder if it can be changed to cut off if voltage goes below 12.3 for example, otherwise even if not using the service battery for auxiliary loads it would soon flatten anyway after a few days of pulse charging the start battery. I think I would prefer something like a voltage sensitive relay that disconnects the two batteries or the link between the two can even be disconnected manually although this wouldn’t be compatible with a smart alternator. I need to try and learn more about this set up before possibly being stranded in the middle of nowhere.
I haven't finished reading this thread but I thought I should add that Ctek told me that the only way to shut off the Smartpass was to disconnect it from the Start Battery. A simple switch or relay can be used. It will not use energy from the Service battery to stay "on". There must also be a 300a fuse going in and coming out of the unit and as close as possible.
I didn't ask directly about any remaining connected consumers as my interest was in having a removable Service battery with everything connected directly to it when needed and not to the Smartpass. The Smartpass does use energy for various functions and will place a drain on the Start battery if left connected - maybe 7a per month or thereabouts (iirc).