After 5 days of not driving my new Prius there
was no response from the power button.
Call the Toyota help number, car was taken to
a dealer who could find nothing wrong, but did
use a jumper to get it running.
Owners manual suggests disabling the smart
key function if vehicle will not be driven "for an
extended period of time", but does not
elaborate on how long that should be.
Therefore, I suggest pushing the disable button
even for overnight to evert 'surprises' the next
day.