Nikon 1 J1 Reference Manual page 39

[] The Camera Clock
The camera clock is less accurate than most watches and household
clocks. Check the clock regularly against more accurate time pieces
and reset as necessary.
The camera clock is powered by an independent, rechargeable
power source, which is charged as necessary when the main battery
is installed or the camera is powered by an optional EP-SC power
connector and EH-Sb AC adapter (_ 161). Three days of charging
will power the clock for about a month. If a message warning that
the clock has been reset is displayed when the camera is turned on,
the clock battery is exhausted and the clock has been reset. Set the
clock to the correct time and date.
19