Canon F1-N Brochure & Specs page 13

2.2 Checking the Battery
Try to make a habit of checking the battery at the followingtimes:
After loading a new battery.
If the shutter won't function with the selftimer/lock lever on "A."
Before and after making many long exposures at slow speeds other than "B."
When you are using the camera at low temperatures.
Before shooting important events.
When the camera is used frequently.
After storing the camera for a long time.
Before going on a trip.
The battery check button also serves to cancel the self-timer, meter reading, illu-
mination of viewfinder information ("LIGHT" setting of meter mode selector), and
shutter operation during long exposures. The circuit is cancelled the moment you
press the button, and the second curtain will close when you remove your finger.
The shutter will not be released if you press the shutter button while pressing the
battery check button.
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2 BATTERY