Went to start our Prius today and the door wouldn't unlock. I thought it might be the key fob but when I manually unlocked it, put the fob in the ignition and got inside, none of the console lights would come on. It turns out that we'd left the dome light on and run the battery down to zero. How can this be, you ask? It's a hybrid car with a 6.5Ah battery. Surely, it should be able to power a crappy roof mounted lightbulb more or less indefinitely. It turns out, however, that that battery just runs the drive system. There's a dinky little lead acid battery that's used to run the onboard electrics and (presumably) start the gas engine. This is easy to run down. Or at least so says the guy who came by to jump start it. Sure would be nice to have some gizmo that detected when you were running down the battery and shut down the internal lights. Not exactly a complicated piece of science to add...