Regarding pressing the Infotainment System Power button twice to turn on the Entertainment System, I have never seen this documented in any Chevrolet documentation or Owner's Manual. On Page 3 of the 2017 MyLink Infotainment System manual there is a reference to Retained Accessory Power (RAP) that directs the reader to the 2017 Owner's Manual. RAP is described on Page 177 of the 2017 Owner's manual but only how to access RAP when turning off the Volt, not activating the Infotainment audio system by pressing the Infotainment Power button twice.So this car doesn't seem to have an "accessory" position for auxiliary power. But if I plug in a USB drive, or just turn on the radio (have to hit the volume button twice), it just comes on. Is that the normal behavior? If I turn it off and exit the car, the power to the USB drive (it lights up) remains for several minutes.
As you noted, the Infotainment system will turn on if you press the Infotainment System Power button twice. I did test the front USB ports and theses USB ports work in this mode. When I plugged in my iPhone to the front USB port the phone indicated it was charging and was immediately connected to CarPlay. I confirmed that the front 12V accessory port does not turn on, I did not test the rear 12V accessory port. I tested the power windows and the power windows do not operate in this mode as they do using RAP. I did not time my test but I was was able to stay connected to CarPlay and Amazon Music via 4G LTE + Wi-Fi for what seemed like longer than 10 minutes. Do you know if the audio system will remain active for up to 10 minutes or until the driver's door is opened, as with RAP, when you press the Infotainment System Power Button twice?