Enable a battery percentage meter to appear in the upper-right corner of your Apple iPhone, iPad or iPod Touch and know precisely how much battery power you have left.
iPhone 3GS and newer or iPad 1 and newer
1. From the Home screen, tap Settings.
2. Choose General.
3. Choose Usage.
4. Switch Battery Percentage to On.
iPod Touch or iPhone 3G and older devices
You’ll have to hack the device using iBackupBot. Please be careful if you intend to follow these steps as doing the wrong thing can damage your device.
1. Connect and sync your iOS device with iTunes on your computer.
2. Download and install iBackupBot on your computer.
3. Disable automatic syncing in iTunes by going to Edit > Preferences > Devices and check Prevent iPods, iPhones and iPads from syncing automatically.
4. Close iTunes and launch iBackupBot.
5. Connect your device to the computer using the USB cable. iBackupBot should detect the device.
6. Select the latest backup you have on the left side.
7. Open the Library/Preferences/com.apple.springboard.plist file by double-clicking on it. Click Cancel on the dialog that appears afterwards.
8. Scroll down to the bottom and place this line right before the </dict> tag.
9. Close and save the file.
10. Check the box next to the line that says Library/Preferences/com.apple.springboard.plist, then click the Restore button at the top bar.
11. Your device will now go through a restore process. When it restarts, the battery meter will appear at the top right portion of the screen.