Right, but it was my understanding that the lithium batteries have heaters built into them to prevent them from ever reaching a low temperature threshold. You

Right, but it was my understanding that the lithium batteries have heaters built into them to prevent them from ever reaching a low temperature threshold. You won't have a button to enable/disable this feature and you probably won't be made aware of its presence by any UI elements. This little piece of hardware would likely be powered whenever the battery temperature reaches a certain point, regardless of whether or not the key were present or the charger plugged in. I'd even be willing to wager that if you left your car dead, with 0% available charge, in a cold parking lot overnight the heaters would still be powered for as long as the batteries could physically maintain them without dropping below 3v/c.