I've come to discover that if I turn on the accessory power in the car, but don't crank it, everything goes fine. But if I crank it immediately from off, it sleeps when the boot sequence is finished. In addition, if I let it boot up under accessory power, then crank it, the display blanks, which I'd expect, then comes back on with a battery icon, but does not sleep.

So it sounds like a voltage issue. Is it likely to be the main power (as opposed to ignition voltage), and, if so, how should I correct that? A better run for the power than coming through the stereo plug where I assume it's coming from now?