Why won't Elsie's Prius won't start after naps

One of the things I really liked about my Toyota Previa was that I could leave the lightswitch on all the time and it would turn off when I got out of the car. BUT, if I turned off the car (to have a nap) and did not open the door, the lights would stay on. I expect this is what is happening to Elsie in her Prius too!

This was the guess, too, when this was discussed over at Priuschat. After a little bit of guessing, someone struck on the headlight suggestion and people went out to confirm that, indeed, the headlights stay on in the Prius until you open the driver’s side door.

See the discussion here:

Whether you are a fan of Subarus or not, the fact remains that Subaru may be the only automaker that does it correctly in terms of headlight shut-off.

When the engine on a Subaru is shut off, the headlights turn off–no door opening is necessary for this shut-off to take place. This just seems so incredibly simple–to have the headlights wired through the ignition switch–that I just don’t know why other car makers don’t do it that way.

Agreed. It’s not clear to me why you would ever want the headlights to stay on when you have the ignition off, but that is the way the Prius works.

My 90 Dodge Colt (Mitsubushi) turned the headlights off whenever you shut off the ignition. Unfortunately, it didn’t shut off the parking lights or the taillights.

The 12V battery in a Prius is about the size used for a motorcycle or riding mower. So there is not much capacity there. It only needs to boot up the Prius’s computers.

She should just leave the car running and put it into park. This way all the electrical systems are still running using the 200V traction battery for power. (The 12V systems also derive their power from the traction battery.) When the battery gets low the engine will start and run a couple of minutes to bring the charge back up. The Prius can run like this for several days on a tank of gas.

Every three years, I have this problem on my 2003 Honda Accord when I stop the car, shut it off, and take a nap or read in the car at the harbor. In my case, it is the automatic headlights that stay on until you activate the shut off switch. I activate the shut off switch by lifting my rear end off the driver car seat, shutting off the lights, then sitting back down again. If I don’t do this, the headlights stay on and the car battery runs down. It is important to remember to do this “right away”, because, once the battery starts going low, there is not enough juice in the battery for the car seat switch to properly shut off. I say “Every three years” because when it happens, I go ahead and replace the battery, and the new battery has enough juice in it to avoid the problem for reasonable amounts of time.

The reason, or at least the way I like the delayed headlight shut off, is when I arrive home in the dark, at night, and get out of my car, the headlights stay on just long enough for me to see my way to the house door and unlock it.

One way to diagnose if the 12V battery is down could be to unlock the doors and see if the rear right door does not unlock.

We had this happen to our 2006 Prius. At some point, the rear right door would not unlock. At first it was every once in a while and then it was more and more often.
We took it to a Toyota dealer and after they dismantled the door and said we should change an actuator, they checked the amperage on the 12V battery and noticed it was going down when something such as unlocking the doors was going on.
So we got a new battery and everything is fine now.