I've been studying this a little more, and it just keeps getting weirder and
weirder. I don't have the full picture yet.
I got one of those 12V power-outlet splitters that has a little voltmeter,
and mounted it so I could see it [could also use an OBD2 app, etc]. Here's
my map to date, *assuming* the car thinks the 12V is fully charged and the
"electricity use" display for electronics has stabilized down around 0.2 kW ...
If you're sitting in Park with lights and climate off and no accessories running,
the 12V rail rises to 14.7 - 14.8. Start driving, or just shift into anything but
Park, it sinks down to 13.3 [a far more reasonable float level] and basically
stays there until you Park again -- EXCEPT, when you regen at all [even in
level 0], it flies right back up to 14.7 or more.
*However*, everything changes when certain 12V loads are turned on, that
bring "electronics" consumption up to 300+W or so. Then, the 12V floats at
14.1V and does *not* change with gear/driving. Headlights will do that, as
will the rear-defroster. The butt-cookers do *not* cause this changed
situation. Neither does an "external" load, like an inverter or 12V appliance
clipped onto the battery. So it's not as simple as bad voltage regulation at
low loads, which would otherwise be a plausible explanation.
The "electronics" figure sees the increase for any additional load, but only
certain types of loads cause the move to 14.1V. My closest theory is that
some loads run through the "intelligent power switch" modules do some kind
of bus feedback that affects the LDC. I haven"t sat there and mapped every
possible accessory's effect, and I don't have a handy map of everything that's
relay-switched or IPS-switched.
_H*