Canon EOS-1D X Mark III DSLR Camera (Body Only) - Manual (Page 58)

Removal
1.
Turn the battery release handle and remove the battery.
Make sure the power switch is set to < > ( ).
Flip out the battery release handle, turn it as shown by the arrow, and
remove the battery.
To prevent short-circuits, always attach the included protective cover
(
) to the battery.
When not using the camera, attach the battery compartment cap ( ).
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