I agree with the turn the lights out comment the only problem is without a ding ding ding reminder my wife tends to forget about them. Maybe if I have her go out when it is 10 degrees and jump the car then she will start remembering more....
It would make sense that the problem involves the ignition switch. I have had another problem that points to the same source. One of the mornings that I went out and found the parking lights on I also found that the steering wheel would not unlock and the key would not turn to the start position.
Having had similar things in the past with other cars I figured I just needed to turn the wheel fully against the limit of the lock and then it would release. Nope did not work. After an hour or better of trying stuff (disconnecting the battery, spraying lock de-icer into the ignition switch, turning the wheel back and forth against the lock, using a heat gun to heat column and ignition switch) and just when I was ready to call and have the thing towed to the dealer I tried one more time. With one hand I turned the key to the right against the point that it would not turn past and kept pressure on it while slowly turning the steering wheel. Then after a little “click” the key and steering wheel released.
I have never had the problem since but kind of feel like it will show up again at the least opportune time.