One issue that typically surfaces after every iOS update is abnormal battery drain.
While the complaints about iPhone 5 battery life are numerous, users should not expect Apple to deliver a permanent fix inside iOS 8.1 or any other iOS 8 update. Unless there is a widespread issue, and while the complaints are numerous these issues don’t appear to be impacting a majority of iPhone users, Apple typically doesn’t react. There’s also a good chance that the battery drain on the iPhone 5 isn’t being caused by iOS 8.
Find Apps Using Your Battery Life
To see what apps are using your iOS 8 battery life, go to Settings -> General -> Usage -> Battery Usage. On this screen you can see what apps use your battery the most in the last 24 hours and in the last 7 days.
You may need to uninstall an app to get better iOS 8 battery life, but the solution may be to avoid using battery hogging apps during the day — like games and watching media.
Turn Off Background App Refresh
One of the first things you can try to get better iOS 8 battery life is turning off Background App Refresh.
Go to Settings -> General -> Background App Refresh -> Turn it all off or off for individual apps.
You can turn Background App Refresh off for all apps or only for certain apps. If you see an app listed with background activity at the top, you may want to simply turn off that app.
Turn Off Push Email
If you use push email to get messages from work as soon as they arrive, you are slowly draining your battery life with every pushed message. If you don’t need email delivered instantly you can turn off push email and get better battery life.
Go to Settings -> Mail , Contacts, Calendars -> Fetch New Data – > Choose the setting for each email account.
Turn Screen Brightness Down
The iOS 8 update didn’t crank up your screen brightness, but this is one of the easiest ways to get better iOS 8 battery life.Swipe up from the bottom of your home screen to open Control Center. Slide the brightness indicator to the left to turn the brightness down.
You can go to Settings -> Display & Brightness -> Auto-Brightness -> Off.
Turn Off 4G LTE
Using the faster 4G LTE network can use more data, and if you are on the edge of coverage this may be the quickest fix for bad iOS 8 battery life. Try turning this off to see if it improves. If it does you may need to leave this off when you are in this area.
Go to Settings -> Cellular -> Enable LTE -> Off.
This is a dramatic step to get better iOS 8 battery life, but if you only need to play games or read a book, and you don’t want the iPhone to die, you can turn on Airplane mode.
Pull the Control Center up from the bottom of your home screen and tap on the small plane icon.
This turns off WiFi and Cellular radios completely, so you can’t do as much with the iPhone or iPad, but the battery lasts longer for offline activities like taking photos and playing games.
Restart the iPhone
If you have not restarted the iPhone since you installed the iOS 8 update or for a few days even, go ahead and turn the iPhone off then back on.
Sometimes a simple restart is enough to stop whatever was causing bad iOS 8 battery life and reset things so the battery will last all day.
Hold the power button down until the screen changes, then slide to the right to power off. After a minute or two hold the power button to turn it back on.