You can extend your battery’s life between charges by turning off features that you don’t need. You can also monitor how applications and system resources consume battery power.Turn off radios that you aren’t using. If you aren’t using Wi-Fi, Bluetooth, or GPS, use the Settings application to turn them off. (The GPS receiver is only turned on when you’re using an application that makes use of it.)

Turn down screen brightness and set a shorter screen timeout. If you don’t need them, turn off automatic syncing for Gmail, Calendar, Contacts, and other applications. Use the Power Control widget to check and control the status of radios, the display brightness, and syncing.

You can check the battery charge level by pressing Menu and touch Settings > About Phone > Status.

The Battery Use screen shows which applications consume the most battery power. You can also use it to turn off applications that you’ve downloaded, if they are consuming too much power. Press Menu and touch Settings > About Phone > Battery Use.

The Battery Use screen lists the applications that have been using the battery, from greatest to least battery use.
The top of the screen displays the time since you were last connected to a charger or, if you’re currently connected to one, how long you were running on battery power before you connected to a charger. Then each application or service that used battery power during that time is displayed, in order of the amount of power they used. Touch an application in the Battery Use screen to learn details about its power consumption.

Different applications offer different kinds of information. Some applications include buttons that open screens with settings to adjust power use.

Google Android 2.2 User’s Guide