My battery recently died when I left my '05 Prius parked for a few days, and had to get it jumped. The hybrid battery was still about half full, so it must be the auxiliary one. I can only come up with one candidate problem, so I'd love to know if I'm on track or not.

When the car is turned off and car is locked then the headlights turn off, and the inside light triggered to door opening & closing turns off. However, the reading light (the lights above the rear-view-mirrow to the left & right of the light triggered by door opening) apparently does not. At least, when I walked around for 5 minutes and came back it was still on.

Now, in my case, after the car was jumped I found that my wife had left the reading light on when she parked the car 3 days ago. Could it be that this is the only light in the car that does not automatically turn off, and hence that tiny light can actually drain the battery if left on for several days? Is this a "feature" or a bug? I'm guessing it's a feature to let me say read in the car when it's turned off, but it ended up being might inconvenient in this case.

Anyways, just want to make sure I diagnosed the problem correctly so that I don't have to wonder if the car will be kaput again tomorrow morning for instance. Thanks in advance.