Sometimes I like to sit in my car while it charges and keep my devices plugged in and charging... will that energy be taken from the HV battery and/or charger, or does it come out of the 12v battery?
Those devices are being powered by the 12V battery. While charging the HV battery, the 12V battery is also being charged. The 12V battery is charged from the HV battery via a DC/DC converter. The amount of energy used by those devices is statistically insignificant, in my opinion.
I agree those devices won't be noticed by the 12V battery, but doesn't the Clarity's DC/DC converter charge the 12V battery only when the Clarity is ON? It would be nice if I'm wrong and it does charge the 12V battery whenever the car is plugged in. I know the traction battery can't be charged when the 12V battery is discharged. However, one time my EVSE did start charging the traction battery, but the next day the 12V battery couldn't do its job. After charging it with a battery charger, the 12V battery seemed fine for a few months. It might have lasted longer, but I changed the 4-year old battery just because. Every week I now make a point of turning ON my seldom-driven Clarity for 30-40 minutes to ensure the 12V battery has a charge.
I have metered charging voltages on the 12V battery under the following conditions: 1) ON Mode 2) READY Mode 3) Vehicle OFF while charging HV battery. The answer your question is: No. The 12V battery is charged in Modes other than ON. Keep in mind that “plugged in” is not necessarily “charging”. The 12V battery will not be charged if the EVSE is connected to the vehicle and charging is scheduled to begin at a later time or if charging is complete.
But know that if your 12V battery doesn't have enough charge to start your Clarity, you won't be able to charge it (or your traction battery) by plugging in to your EVSE. In this post there is a photo of myself on the floor of my tiny garage, worming my way alongside my Clarity towards the barely-open hood to connect a charger to the 12V battery. I learned the hard way that I can't leave my Clarity for two months without driving it, or without at least not turning it on periodically to give the DC-to-DC converter a chance to recharge the 12V battery from the traction battery (which doesn't seem to notice two months of waiting).
The 12V battery is the key to the kingdom. Even with the availability of a 120V or 240V power source, or up to 17kWh’s of stored energy in the lithium battery, there is no way to access that energy without a 12V power supply to enable the appropriate circuitry. A charged, lithium jump pack is a simple and reliable solution to this potential issue. Provided that there is easy access to the battery, of course.
