I just did an experiment. Drove the car in EV mode until the ICE was forced to come on shortly before arriving home due to low battery. Battery reported 10% in the app when I parked. ICE shut down when I shifted to park, but I didn't turn the car off, just handed the remote to my wife to simulate leaving walking away with the car turned on. I left the heat pump on (heating to 70 with an outdoor temperature in the high 50s) and turned on the seat heaters to speed up the test.
The car gradually ran down the high voltage battery pack until, about 30 minutes later at what I think was the bottom of 2%, it turned the ICE back on. (I say I think because I believe it shut off the cellular communication at that point; it no longer would connect to the car until I had plugged it in to charge later; seems like maybe the HondaLink system runs off the high voltage pack and shuts down at 1% SOC to protect the battery.) At no time did it stop floating the 12V aux battery; I checked it a couple times and it was sitting comfortably at 14.5V even with the heat pump, a couple of seat heaters, and the radio on.
So in this case, it sure looked like the car was just going to keep cycling the ICE to keep it from running down the battery. This doesn't fit at all with what this thread is describing unless:
- The car will eventually shut down the ICE and stop using the HV battery after some timeout greater than 30 minutes, but not shut off the auxiliary power, so it will end up running down the 12V battery at that point.
- The car was aware someone was sitting in it, and behaves differently in that situation than if it's empty.
- The thread starter actually had the car in Accessory mode rather that just on.
Since I originally joined this forum to ask questions about the 12V DC system when left on for an extended period of time in exactly this situation--I'm hoping to hook an inverter to the 12V battery to act as a backup for a few circuits in my house in lieu of a portable generator--I'm
very curious if the car will indeed run itself dead if left on in park for several hours. (Also if it automatically shuts off, and if so what the timeout is; leaving it in neutral with the parking brake set would be a possible workaround for us edge cases that don't want it to turn off.)
Also, an aside, the heat pump compressor cycles surprisingly frequently (probably on and back off every 10-15 seconds) at some temperatures. You really can't hear it inside the car, but with the hood open it's pretty loud.
Second aside: I really can't believe that it's 2018 and cars can drive themselves, park themselves, and maintain a complex hybrid drivetrain, but can't manage to shut off accessory mode before the 12V battery is too dead to start the car. Seriously, guys, this has been a problem since the starter motor was invented, and it would take about an hour to code the logic using sensors that the car already has.