Canon AE-1 Instructions Manual page 22

How to Check the Battery
T o check the pmver level of the battery,
press the battery check button on the top of
the camera while watching the meter needle
in the viewfinder. I f the meter needle rests
below or coincides with the index opposite
the
5.6 flstop, the power level is sufficient.
If the needle rests above the index, replace
the battery with a new one of the prescribed
type. When a new battery with full voltage is
used, the needle will swing below the
4
f/stop. The weaker the battery, the closer
the needle comes t o the index.
If the meter needle fails t o stabilize
within about three seconds, the battery is
near exhaustion and should be reDlaced.