Save battery power by enabling your BlackBerry Pearl to automatically power on and off. It might be handy for you to configure it to power off late at night and power on in the morning. Here’s how to do it in software version 4.1 and above.
1. On the Home screen, select Options.
2. In Device Options, select Auto On/Off.
3. Change the Weekday field to Enabled.
4. Specify the times when the BlackBerry device should turn on and off on weekdays.
5. Change the Weekend field to Enabled.
6. Enter the times when the device should turn on and off on weekends.
7. Press the Menu key.
8. Click Save.
Source: BlackBerry Pearl Users Guide