There has to be. If you let the deck sit w/o powering it on for an extended period of time it loses time and date.
I always check a day or so before a show and if time and date are not retained I leave the deck powered on and on hold (not recording) overnight with a set of used batteries or plugged in to the wall wart and the next day it retains the time/date settings after power cycling or swapping batteries.
I should note all other settings seem to save to NVRAM and are retained regardless of whether the clock gets reset or not.
Hope this helps.