One way to make sure your batteries stay charged is to turn off your phone every night. The blackberry Storm has a feature that lets you set a time for your phone to turn off every night. You can also set a time for it to automatically turn back on. Not sure if other blackberry's have this feature or not.

To set this on the Storm go to the device options and click on Auto On/Off. There are then separate sections to control this behavior on weekdays and on weekends. Once you enable this feature you can set the time for your Storm to automatically turn on and off. Once you make changes here, hit the Menu key and select Save to save your changes.