There are several ways you can try to fix battery drain issue if you had battery drain issues on iPhone, iPod Touch or iPad after upgrading to iOS 8.4.1.
Here are some steps to fix battery drain issues in iOS 8.4.1:
Recalibrate device’s battery: Charge the device to 100 percent then drain the battery until device shuts itself off. Plug the device back in and charge it back to 100 percent without interruption. Reset device by holding both the home and power buttons until device restarts itself, ignoring the “slide to power off” slider. Your battery should be recalibrated.
Perform Hard Reboot: By holding the Power and Home button till iOS device vibrates and restarts automatically, ignoring the “slide to power off” slider.
Reset all settings to iOS defaults: Go to Settings > General > Reset > Reset All Settings. Data will not be erased.
Restore/Clean Install of iOS 8.4.1: Download the respective IPSW file for iOS device. Plug your device into iTunes, navigate to device screen, then option-click (shift-click in Windows) the Restore button, selecting IPSW file you downloaded. Performing a Clean Install/Restore will sometimes help improve battery life.
Manage which apps use Location Services: Go to Settings > Privacy > Location Services and either switch Location Services off, or prune your list of apps which have access to your location. Make sure Location Services isn’t enabled all the time.
If battery drain is still happen after performing all the above steps, then you may need to take your iOS device to Apple Store.