I've no idea what the right temperature is, I guess all I'm saying is we have a simple on/off control. Turn on HVAC or Precondition or call it what you will, and the car will do stuff - if the cabin is too hot it will cool it, if its too cold it will heat it, if the battery is below what the car thinks it wants it to be, it will heat it. All of these things use energy. If range matters on that trip, and you're plugged in, then any energy needed to get the car to a place it's happy with will come from the mains, it might not need much, or it might need a lot. We've little to no control over simply turning it on or off. I think we're over thinking the cabin temps etc. If it was a frosty night but the sun has come up and the cabin has warmed up as a result but the battery is still cold, the precondition/hvac should still heat up the battery if it thinks it needs to even if the cabin was prety much at the right temp already.