Airliners are regularly and routinely shut down. "Cold and dark" is a common startup procedure for the first flight of the day.

A parked Aircraft is not kept powered when there are no maintenance or other routine(cleaning/checks/certification/preparation/restocking etc.)

It is very surprising that how a lot of comments here claim the contrary.

Even when parked for next flight, until resupply and cargo routines are declared, it is also not powered.