Canon EOS 7D - Manual (Page 251)

251
The date/time (back-up) battery maintains the camera’s date and time.
Its service life is about 5 years. If you turn on the power and the date/
time is reset, replace the back-up battery with a new CR1616 lithium
battery as described below.
The date/time/zone setting will be reset, so be sure to set the
correct date/time/zone (p.43).
1
Set the power switch to <2>.
2
Remove the battery.
3
Take off the battery holder.
4
Replace the battery.
Make sure the battery is in the proper
+ – orientation.
5
Insert the battery holder.
Then load the battery and close the
cover.
Replacing the Date/Time Battery
(+) ( – )
For the date/time battery, be sure to use a CR1616 lithium battery.