Whenever there's a new iOS update, there are a lot of improvements and changes in the new version. Sometimes these new features are on by default and can end up using more battery, making it look like the new version of iOS isn't behaving as well as the old one. Listed below are a few ways to trim down some extraneous activity that could be gnawing on your battery. Keep in mind these are only suggestions, commonly overlooked settings and options that could use more battery than you might realize.
First, see if you have an actual battery issue. Here's how to check: Go to Settings > General > Usage and write down what your standby and usage times are right now. Then press the Power button on top of the phone to lock your screen. This is the hardest part of any of the instructions: Wait at least five minutes with no phone use, not even pressing the home button to check the time. After five minutes, go back to Settings -> General -> Usage and compare notes. You should see that standby time went up five minutes and usage time is likely the same but it might have gone up (because it rolled over to the next minute). If it's more than one minute, there may be an issue.
Next up is a new feature in iOS 8. Check usage yourself in Settings -> General -> Usage -> Battery Usage, as shown in this screenshot:
View of battery usage preferences in iOS 8.
Here, you can see what is actually hitting your battery hardest. You may be able to eliminate the top offenders pretty easily, but even if you keep them, now you know what they are, and knowing IS half the battle. Here's my iPhone 5s's Battery Usage:
Actual Battery Usage! How Useful!
A common issue is that email (most commonly from Exchange accounts) set to push can get caught and drain the battery. You can gain some savings by going to Settings -> Mail, Contacts, and Calendars -> Fetch New Data and disabling Push email. It can be set to check every 15 minutes, and after that repeat the above test to see if it helps.
Also check Settings -> General -> Handoff & Suggested Apps. Handoff doesn't help you much if you only have one iOS device, since the WWDC-demonstrated features that work with your Mac aren't available until Yosemite is officially released (on the beta your mileage may vary). There's also a chance you don't want your iPad to ring every time you get a phone call, so adjust this one accordingly.
Handoff preferences in iOS 8.
With a new device, even restoring a previous backup sometimes doesn't get everything. There are things you may want to double check. Start with verifying your brightness settings are what you want them to be. Primarily, turn down the screen as much as you can and make sure auto-brightness is enabled, that way if you do end up someplace very bright or very dim, your screen will adjust accordingly.
Other settings to double check are listed below:
Settings -> Privacy -> Location Services
Location services allow apps to know where you are. That uses your GPS, and that takes power. Turning them off entirely will make your iPhone more efficient, but less useful. But, you can decide which apps have access to Location Services. For the sake of your theoretical privacy and battery management, only allow those apps you truly want or need to have access to your location have it.
Settings -> Privacy -> Location Services - System Services (at the very bottom of the list)
These settings are for all your iOS system-wide features. Compass, location-based iAds, frequent locations, new features like Popular-near-me, and the like. Again, disabling any or all of these will make your iPhone more efficient, but less useful. Use what you need and want, and turn everything else off.
Location Services - System Services
Settings -> General -> Background app refresh
Background app refresh is a key usability feature in iOS—it allows your apps to do things in the background. Apple set it up in the most efficient way possible, but it does still require power. I would advise you to be very careful about what you enable and disable here, because it will affect the way your apps work.
Settings -> General -> Autolock
When you put your phone down, it stays on. That's the epitome of wasted battery life. But, you can control how long it stays on, either 1, 2, 3, 4, or 5 minutes. Or never, if you just hate your battery with a deep and abiding passion normally reserved for your arch enemy. What setting works for you will be highly subjective. For some people, 1 minute will work just fine. Others might need more. Play around and find the setting that works best for you, but remember that less (time on without you using it) is more (battery life).
Settings -> Safari -> Preload Top Hit
This is another new feature in iOS 8. When you search in Safari, it will give you the top hits automatically, and preloading that makes it faster. It also sucks up juice. This is such a new feature, we aren't necessarily advising that you turn it off. Apple appears to be in the process of disrupting the way we search with this and other features in iOS 8 and OS X Yosemite, and you might want to try it out before turning it off.
Preload Top Hits
Settings -> Wi-Fi -> Ask to Join Networks
Ask to Join Networks is either the best thing ever or the devil incarnate, depending on your point of view. When enabled, iOS 8 will constantly look for new Wi-Fi networks and ask to join them the second you try to invoke an Internet connection. If you like your iPhone constantly popping up requests to join networks, you might enjoy this. If not, turn it off. Constantly looking for networks requires power.
Settings -> iTunes & App Store -> Automatic Downloads
Starting in iOS 7, Apple allowed app updates to be downloaded in the background. More often than not, it's very convenient, but it's another feature that requires power. If you don't mind managing updates on your own, or if you need to eke out every second battery life that you can, turn this feature off.
And if you're still not able to sort it out, try restoring to factory settings. This time after walking through settings, don't restore from backup and just start over from zero. You can always restore from backup later if you want to, but this is a good last-ditch test to try before taking your phone in for a professional examination.