Sony Reader PRS-700 Guide De L'utilisateur page 22

You can verify the remaining battery power by checking the
indicator in the bottom left of the screen. Charge the battery
when remaining power is low (the fewer black segments
indicated, the lower the remaining power).
Note
 If the remaining battery power is low, the following warning
appears. Charge the battery.
If you continue to use without charging, the following warning
appears, and the Reader will shutdown automatically.
Charge the Reader and turn it on again.
22
US