The electronics runs off the 12 volt battery, not the high voltage battery. The electronics that has a small drain on the 12 volt battery are the systems that secure the car, locks, sensors, and radio receivers for your remotes among others while the car is parked and locked. As the 12 volt battery is drained from these devices, it has to be recharged by the HV source (through a 12v regulator) which is being charged by your EVSE which will maintain the HV battery at a set % of maximum. So, while the EVSE doesn't run the electronics and other low voltage devices directly it does draw power from the HV battery that will be kept to the % you set it at. If the HV battery is not plugged in for an extended period of time the drain is said to be about 1% per day as the HV battery replenishes the 12v battery to run the electronics etc.
If you install 24 hour monitoring software you can see these times when the EVSE replenishes the HV battery that is drained to the set %. All this is why Tesla wants you to keep your car plugged in when you won't be using the car for extended periods of time to avoid the 12v battery from eventually going dead which can ruin it.
If you leave the car not plugged in, to prevent the HV battery from being drained it quits recharging the 12v battery when the HV is below a certain %, Then the 12v battery will be drained. When that happens you can't unlock the car. There is a port in the front bumper you can open which you can apply 12v to open the Frunk. Then you can gain access to the 12v battery and charge it up enough to unlock the car, or if necessary replace it.
I suggest you read your manual as this stuff is explained.