Tip: How to Give Your BlackBerry a Rest While You Sleep
And if you don't want it beeping and ringing and generally disturbing your leisurely weekend mornings, fear not—the feature has separate settings for weekdays and weekends.
First, got to Home-->BlackBerry Menu-->Options-->Auto On/Off.
Then set the on and off times for week days and weekends.
Next, be sure to save your settings—either by pressing the back button and selecting "save" or by using the BlackBerry Menu button and selecting Save.
Here's what you do:
If you use the Auto On/Off option your battery should last longer, but it doesn't mean you can skip the charging. So you may want to set a "plug in phone" reminder to come up every two days or so just before the device automatically shuts off.