If your N-Series device in not holding correct date \ time or the time is being represented  such as 01 Jan 1970.  It is likely that the battery had failed.

You can correct this by using NTP (Network Time Protocol) settings on the N-Series device

·         Open the Setup UI, go to Preferences > Display/Time

·         Uncheck the ‘Set date/time automatically’ check-box

·         Verify the Date and Time or adjust them, if the values are wrong

·         Click the ‘Apply now’ button; This will set the hardware clock to current system time

·         Select the ‘Set date/time automatically check-box again, if necessary

·         Click the ‘Save’ button

or

You can see the attached document for the procedure to replace the battery in the device.