It was 48 degrees in my garage when I took a package out of the Prius. The next morning I realized I had not closed the hatch. I figured I'd screwed up and needed a jump start. The car started right up and I've had no problems since. Why? I don't use the the rear hatch courtesy light but the dome light comes on when I open the hatch. Why didn't the battery drain? I do think the dome light was off in the morning until I opened the driver door.
My guess is that your 12V battery was in better shape and more fully charged as compared to some other owners' batteries.
Interesting...my '05 was about 2-1/2 years old when I had a similar experience. I had delivered some stuff to our new homesite, but had left the hatch not fully latched. About 4-5 hours later, I passed the car, heard a beeping, and happened to see the hatch light lighted. When the car was powered up, it showed only one bar on the battery monitor, but the ICE immediately started and started charging the battery. Like you, I wonder what would have happened had the light been left on for 8-10 hours. Thanks for starting this thread. BTW, my OEM 12V battery lasted over 5 years, 2-1/2 years after my incident.
The battery monitor has nothing to do with the 12V battery. It's for the traction battery, the 201V one. A healthy 12V battery will have no problem powering the interior lights for 12 hours. It's a 35 or so A-Hr battery. The lights draw less than 1A typically, unless you have them -ALL- on! So you will drain 12 A-Hr out of a 35 AHr battery. It will still be fine. Just don't do it often. It's hard on the battery. Most "dead battery" problems are from one light left on for several days or from a weak battery being "challenged" by a light for one overnight event. If you manage to leave the headlamps on, that's another story! They will drain the 12V battery in a few hours! So beware. Note that it can take a long time for the car to recharge the 12V battery. You really should have it in "ready" for at least 3-4 hours to get the charge level up to a safe level after a discharge "event".
I can honestly say the car will start the next day after you leave the drivers door open all night. I put the girlscout cookies in the car late last night and found I had not closed all the doors when I was done. Both dome lights were on in the morning. I would estimate about 10 hours overnight in the midwest (10 - 15F). Of course my battery is fairly new (or it was anyway).
