FBOs find batteried dead because people leave the master on.
Too tired or distracted to complete a proper shutdown checklist. As for
the cig lighter socket, Cessna and the FAA issued an AD years ago to
have them disconnected as they presented a fire risk; there was no
breaker for the socket. They did allow the owner, if he desired, to put
an inline fuse in the line to the socket if he needed it for other
things like intercoms and such.

Dan