Canon EOS-1DS MARK III Instruction Manual page 81

Replacing the DatelTime Battery
The date/time (back=up) battery maintains the camera's date and time,
Its service life is about 5 year& If the date/time is reset when the battery
is replaced, replace the back=up battery with a new CR2025 lithium
battery as described below,
The dateRime setting will also be reset, so be sure to set the
correct dateRime.
Set the power switch to <OFF>
and remove the battery pack.
_ The back=up battery is on the ceiling
of the battery compartment.
_ emove the back-up battery
cover,
®_ Use a small screwdriver to loosen the
screw and remove the coveL
®_ Be careful not to lose the cover and screw,
'_ Remove the battery.
_ Install a new back-up battery.
_ The plus side of the battery must face
up.
_ Attach the cover.
@For the dateiiirne battery, be sure i0 use a CR2025 lithium batterYl
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