I can't fully answer your question but what I can tell you is wiggling the keycard in the ZE40's slot is enough to keep the radio alive for longer. I believe it's on a timer, so it's not soley switch dependant.
On ZE50 there is APC mode for exactly this use case (well I think it was more for ZE50 Van and running things off the 12V cigarette lighter.. but same effect).
On ZE50 there is APC mode for exactly this use case (well I think it was more for ZE50 Van and running things off the 12V cigarette lighter.. but same effect).
