1. Test battery life on standby (put your device down)
Whenever you update to a new version of iOS or get an new iPhone, it's only natural to want to try out all the new features. Maybe it's Extensibility or Continuity, maybe it's Touch ID apps or Photos editing, or simply all the new, cool iOS 8 apps, you'll likely do a lot more on update or upgrade day than you did on any normal day. Yet every time you sling sound bites, interact with notifications, pull down widgets, switch between custom keyboards, or do any one of a hundred other fun new things, the screen will light up, the radios will fire, and the battery will drain.
The point is, it's almost impossible to realistically assess a change in battery life if you've also changed your usage pattern. in other words, if you're battery feels like it's only lasting half as long, the first step to fixing it is figuring out if you're using it twice as much.
So, before you do anything else, note down how much battery life you have left. Then put your device down for 10-20 minutes. When you pick it back up, note down how much battery life you have left again. f there isn't a big change while in standby, you're probably okay and your battery life will return to normal when your usage returns to normal (after the novelty wears off). If your device continued to drain, and drain fast, even when you weren't using it, there's a problem.
2: Check for software problems
If, in general, your battery life is consistently short and you're basically just watching the indicator drain down before your eyes, here are some things to try, in order of how easy they are to do.
Check battery usage: iOS 8 brings something similar to OS X Mavericks-style battery usage — aka battery shaming — to the iPhone and iPad. Located in the Settings, General, Usage section, it tells you which apps and system services are using power, and how much. Obviously the ones using the most power are doing something wrong and should be shut down, right? Wrong. Like many things, the answer is far more complex and nuanced than simple power bad, quit good. Here's how battery usage monitoring works on iOS 8.
Check your cell signal. If you're in an area of weak signal, or at the edge of LTE or 3G support, your iPhone's radio could be screaming away on full power just trying to stay on the network, or switching between connection types, and wasting a lot of power. Good LTE signal is more power efficient than good 3G signal (because the radio can fire up, do its job, and power down much, much quicker), but bad LTE signal is just as bad as bad 3G, which is terrible. If you're at the edge of LTE, switch to 3G. If you're almost off the grid, turn off the radio unless and until you need it. Then get back to world as fast as you can!
Reset your network settings. If you're getting a bad cell signal or your carrier is working on towers causing your signal to jump, resetting your network settings can sometimes help alleviate issues. Try this before anything else if you're noticing only 1-2 bars of signal in certain areas you frequent.
Quit power hungry apps. Double-click the Home Button to activate the multitasking car view and quit, hold your finger down on power-hungry apps, and then fling them off the screen to close them. This is key for apps like VoIP (like Skype), streaming audio (like Pandora), or navigation (like TomTom). Anything running all the time will drain battery. That's how batteries work. Some apps can also fail to sleep properly when not in use. If quitting Facebook or Skype stops your battery drain, quit Facebook or Skype. After some experimentation you'll find occasional and chronic offenders alike. Here's how to quit/kill apps in iOS 8
Restart/reset your device. If you haven't rebooted in a while, give it a try. There could be a rogue process or something else doing what it shouldn't be doing, and a restart can often fix that. Here's how to reboot)
Power cycle. About once a month, and certainly if you think you're having problems, you should completely drain your iPhone, iPod touch, or iPad's battery -- drain it until it shuts down on its own -- and then charge it back up to full. That re-calibrates the battery indicator and you'll get a more realistic idea of what your levels are. can solve by either swapping it for another device or otherwise figuring out a fix.
Go to the Apple Store. Sometimes you do get a lemon, or your iPhone or iPad develops a real problem that only Apple can fix — by servicing or replacing your device.
3. Restore your device as new (not from backup)
The single biggest cause of battery life problems with iOS devices occurs when they are restored from backup and not set up as new devices. Whether it's cruft or corruption, bit rot or simply bad bits, a clean install as a new device — incredible pain in the butt though it may be — is usually the best fix for any battery life issues. This is the nuclear option. You will have to set up absolutely everything again, and you will lose all your saved data like game levels, but in most cases your battery life will be better than ever.
How to restore and set up your device as new
4. Turn off Location Services, Background App Refresh, and Push Notifications
Anything running on your iPhone, iPod touch, or iPad uses up the battery. So if you've tried everything else and it turns out you're just using your device more than the battery will allow for the length of time you need to use it, you'll need to make some hard choices. You'll need to stop using some of the features you don't really need in order to keep using the ones you do. The more you turn off, the longer your batter will last -- but of course the less you'll be able to do. It's a balancing act but one that can help you squeeze out a little extra juice when you really need it.
Turn off Location Services. GPS requires a huge amount of power, especially for things like turn-by-turn navigation and Find my Friends tracking. If you suspect location services are chewing up your battery when you're not using them, go to Settings, Privacy, Location Services, and turn off any app and system service you really don't need tracking or using your location.
Turn off Background app and content refresh: Background Refresh does everything it can to coalesce and schedule downloads to minimize battery drain. However, any background download will use battery. If you need power more than you need fresh content, go to Settings, General, Background App Refresh shows you everything you can turn off. Also go to Settings, App Store and turn of automatic app and content downloads. Here's how to turn off Background Refresh
Turn off Push Notifications. Likewise, go to Settings, Notifications, and turn off any app you don't care to be alerted about.
There are some old tricks you can try when you're in a jam as well, and the new Control Center makes it really easy to do many of these really quickly now!
Set Auto-Lock to 1 minute
Turn off any extra sounds, like keyboard clicks
Turn off the iPod EQ
Use headphones instead of the speaker if you have to listen to audio or music
Turn down the screen brightness
Turn off Bluetooth when not using it
Turn off Wi-Fi when not using it
Set all email, calendar, and contacts accounts to "Fetch" (turn off Push)
5. Airplane mode!
If you're really desperate, put your iPhone or iPad in Airplane Mode and save the radios for when you need them. If you're really desperate, you can also turn your device completely off until you need it (it will still use a tiny amount of power but far, far less than anything else).
How to get more help with your iOS 8 battery life
If you need more help, or just more personalized help, with trouble shooting your iOS 7.1 battery life problems head on over to the iMore forums! Either way, tell me — how's your battery life under iOS 7.1, did any of my tips help, and have you got any of your own to share?