It's hard to say how long it takes. It is a car we don't drive that much, but I believe it has happened when the car just sat overnight. On other occasions, it sat for at least a day or two without being driven, maybe even a few days. However, the car has sat for as long as a few weeks without being started but started right up. This problem seems intermittent.
It is my mother in law's car, but she has stopped driving and my wife and I and one friend drive the car at times. Sometimes we drive it every day, at other times it may sit for several days without being started. As I said above, it has even sat for several weeks and started right up.
Is there something in the alternator or voltage regulator that could be defective and causing the draw to happen intermittently? The battery that is in there now is only about five or six weeks old. btw, when the battery goes dead, it goes COMPLETELY dead.
There is something strange going on. I have dealt with cars, jeeps and boats enough in my 70 years to know that this is not normal and is intermittent. The first time or two it happened, I though maybe someone inadvertently left the headlights or dome light on. However, I know now that that isn't what is happening.
We blamed it on a defective battery the first couple of times, but we are now on battery number 3 in six months and it is still happening.