I see. IMO, it's counterintuitive to think that the charger voltage declines as a battery reaches capacity. For instance, during SpC the charger tracks the battery voltage and both rise in step. I guess 12 V is just different.
So the higher the voltage, the lower the capacity of the 12 V. Interesting. What is a normal value range (DC/DC) for a C&D deep cycle in a new Tesla?
The higher the voltage the lower the capacity is not true as an absolute statement. I think you maybe understood but in case someone reads this and is confused I'm going to toss some too long stuff in here.
Let me try to restate this.
12v batteries are very low capacity vs the HV pack in an EV. They vary in voltage greatly without load vs with load. So the same battery with no change in actual capacity or state of charge can show up as:
Voltage 1 no load
Voltage 2 with minor load
Voltage 3 with more load
Voltage 4 with even more load
Voltage 5 with a temperature change.
So to test health of a 12v battery you can't just look at voltage.
Now cars computer systems only have voltage to judge the SOC by and if they see it low they try to raise it. But they do so by adding another voltage to the circuit. The difference between the voltage of the 12v battery and the voltage the inverter is supplying determines if the system is charging the 12v battery.
Ideally to test the voltage of a 12v you would pull it out of the car and let it rest for a day, then check the voltage with no load, and then check the voltage with a known load.
In reality we have the battery tied into various loads and not resting ever, it's pretty much always being drained or charged non stop. 99% of the time the loads will be imbalanced enough to cause it to go up or down barring the computer trying to compensate. If you are watching the voltage of the inverter or the voltage of the bus you are watching multiple variable equations in real time. The number spied is almost never going to match what you would get if you tested the inverter without a battery or the battery without the inverter.
So yeah I'm implying that the inverter output will go up at the computer request to try and charge the battery if the battery needs it and the more you see that the worse the battery is likely to be. But it's also possible that "vampire loads" have changed and the inverter is just keeping the battery healthy. You can't be sure if the charging activity is proactive or reactive.
It's designed to be proactive. But if it were successfully proactive on the grand scale people wouldn't be changing 12v batteries in 12-24 months.
I have no idea what normal charging is on the Tesla. I'm used to watching it on the Prius and Leaf which both tend to undercharge the 12v in normal driving. I get the impression Tesla is doing a better job with managing the 12v but is also putting way more demand on it and unfortunately churning through 12v batteries quicker than a Toyota or Nissan would.