Canon REBEL T3I EOS 600D User Manual page 279

The battery becomes exhausted quickly.
Use a fully-charged battery pack (p.26).
The rechargeable battery pack performance will degrade over
repeated use. Purchase a new one.
If you use Live View shooting or shoot movies for a prolonged period
(p.123, 141), the number of possible shots will decrease.
If you hold down the shutter button for a long time or often use only the
AF without taking pictures, the number of possible shots will decrease.
If you often use the LCD monitor, the number of possible shots will
decrease.
If you use the lens Image Stabilizer, the number of possible shots will
decrease.
The camera turns off by itself.
Auto power off is in effect. If you do not want auto power off to take
effect, set [5 Auto power off] to [Off] (p.167).
Even if [5 Auto power off] has been set to [Off], the LCD monitor will
still turn off after the camera is idle for 30 min. Press the <B>
button to turn on the LCD monitor.
Shooting-Related Problems
No images can be shot nor recorded.
The card is not properly inserted (p.29).
If the card is full, replace the card or delete unnecessary images to
make room (p.29, 224).
If you try to focus in the One-Shot AF mode while the focus
confirmation light <o> in the viewfinder blinks, a picture cannot be
taken. Press the shutter button halfway again to focus, or focus
manually (p.40, 87).
Slide the card's write-protect switch to the Write/Erase setting (p.29).
Troubleshooting Guide
279