There have been widespread complaints that iOS 8 has been draining iPhone batteries, leading to shorter battery life. If that's happening to you, fear not: I've got ways to easily increase your phone's battery life.
Turn iPhone location services off
Location services and the GPS can use up plenty of battery life. Depending on how you use your device, you may not need location services on most of the time. So turning them off, and only turning them on when you need them can save plenty of battery life. Go to Settings--> Privacy--> Location Services and turn Location Services off.
If you prefer, you can instead have apps do the work for you, and only use Location Services when they need it, saving you considerable power. You'd be surprised how many apps use these services in the background when they only need to access them rarely. To do it, go to Settings--> Privacy--> Location Services. With Location Services turned on you'll see a list of all of the apps that use the services. Tap any to customize how it uses them. Many only give you two choices, Always or Never, but some have a third choice, "While Using the App." For those that that don't need location services, switch them to Never. For those with the third choice, select "While Using the App."
Identify battery-hogging apps
Some apps suck up a lot more battery juice than others. So check if you've got any battery-hoggers with a new iOS 8 feature. Launch the Settings app, then select General-->Usage-->Battery Usage. You'll see you which apps have used the most of your battery over the last 24 hours and the last two days. The list includes all your apps and the percentage of the battery each has used, with the heaviest users at the top of the list.
When you do that, take action. You can delete the biggest battery-hoggers, or reduce the amount of time you use them. Or you can modify the way you use them, for example by telling the app not to do things such as download data in the background. (More information on that, below.)
Change display settings
It takes a lot of electricity to power your display. So don't be surprised if that's regularly at the top or near the top of battery-killers. There's a lot you can do to reduce how much of your battery it uses. First, reduce the screen's brightness. To do it, Open Control Center by sliding up from the bottom of the screen. Then move the brightness slider to the left to make the screen less bright.
Next, turn off the Auto-Brightness setting. This setting automatically adjusts your display to the current ambient light level. But if you turn it off, you can keep the setting low, and only turn it higher manually when you need it. Go to Settings--> Display & Brightness--> Auto-Brightness and change it to Off.
Turn off Bluetooth
You'd be surprised at how much battery life Bluetooth uses. The odds are that you don't need it that much -- perhaps for a headset or for use with an external speaker. So turn it off, and then only turn it on when you need it. To do it, select Settings-->Bluetooth and then turn it off.
Turn off background data use
Apps that download data in the background can possibly eat up battery life. You can either turn it off for all apps, or select which you want to download data in the background and which you don't. Go to Settings-->General--> Background App Refresh and turn the setting to Off to turn if off for all apps. If you prefer to leave it on for some and off for others, leave it on, then tap any app for which you want to turn it off and set it to off.
Stop push email
Some iOS devices use up too much electricity when grabbing email in the background. You can turn it off altogether, or change how often your device checks for mail. Go to Settings-->Mail, Contacts, Calendars--> Fetch New Data. It lists all of your accounts and how each checks for new mail. For each, you'll see Push, Fetch, or Manual. With Push, your device checks for email constantly and notifies when you get a new one. Fetch will check on a regular schedule, and you can change that -- your choices are 15 minutes, 30 minutes, and hourly. Checking manually will save the most battery life.