If the batteries do fail, the EF can still be used manually from 1/ 2 - 1/1000 sec. The Variable Aperture AE control will not operate, but you can manually adjust the aperture ring of the lens. A basic exposure guide to follow for bright sunlight (with distinct shadows) is to make a fraction representing the shutter speed needed at f/16 by putting a "one" over the film's ASA rating.
This indicates that the film has left the multi-slot take-up spool. Turn the rewind crank one or two more revolutions to completely rewind the top of the film leader back into the cartridge. The pull up the rewind knob to open the camera back and lift out the cartridge.
Situations where the Image Stabilizer is not effective EF100-400mm F4.5-5.6L IS USM In MODE 1: panning shots where there is considerable camera movement. In MODE 1: shots from vehicles, where there is considerable motion. In MODE 2 : shots other than panning shots.