I tried to start my car today and the electric system was dead. When I jumped the car it started right up. At first I thought my wife had left the car running all night but I noticed their was still alot of gas in. Their was a door slightly ajar so maybe a light was left on? If a car is left on will it keep the battery charged enough until it runs out of fuel? Does the Prius know to shut off power ahead of time when the 12V gets low? soon as I jumped the car I was able to turn it off immediately and start it up without a jump. This is unlike other cars I had where you had to drive them around immediately or you would have to jump start it again.