Logging Energy Usage in an iOS Device
Log energy-related data on an iOS device while the device is in normal use in order to take realistic measurements.
Go to Settings > Developer > Logging and turn on logging.
Exercise your device as if you were a user.
After capturing the data, turn off developer logging.
With Energy Diagnostics Logging on, your iOS device records energy-related data unobtrusively while the device is used. Because logging is efficient, you can log all day. Logging continues while the iOS device is in sleep mode. However if the device battery runs dry or the iOS Device is powered off, the log data is lost.
The Developer Setting appears only after the device is provisioned for development. The setting disappears after the device has been rebooted. Connecting the device to Xcode or Instruments restores the setting.
After sufficient energy usage events have been logged they can be analyzed by importing the log data from the phone to the Xcode Instruments Energy Diagnostics template.