Sandy says: I've taken the plunge and got a Iphone 6...BUT the battery is discharging very quickly...do you know why?
There are quite a few things you can try to resolve this. It may just be a setting (or settings) that need changing, or there may be an underlying problem that is causing this issue.
Try a Forced Reboot
This my 'first port of call' when my iPad or iPhone is behaving in a way that seems a bit strange or the battery seems to draining too fast.
Hold down the Home Button and Sleep Switch at the same time for 10 seconds or so, until the screen goes black and the Apple appears, then let go.
I have found that this has resolved battery problems in the past, especially after an ealier iOS 8 update.
Check what apps or system features are using up all your battery
A new feature of iOS 8 was an area in Settings that allows you to see what apps and features have been using up your device's battery - so that you can hopefully identify the culprit and close it down.
For example, there are some apps that may be running in 'background' mode, consuming data and battery - without you realising this.
Go to Settings → General → Usage → Battery Usage
If you find an app that seems to be using up a lot of battery, bring up your task switcher and swipe the applicable app up to close it.
If it is a 'background activity' that is causing a problem, you may need to delve a bit deeper into your Settings to turn off the feature or stop it running in background. (See further on this below.)
Turn off 'background app refresh' for apps that don't need it
iOS 7 introduced a new area in Settings → General called Background App Refresh.
This feature 'allows apps to refresh their content when on Wi-Fi or cellular in background'.
You can turn the feature off for individual apps, or just turn it off at the top for all apps on your device.
I found the likes of Facebook to be particularly bad for battery (and data) drainage.
I have turned this feature off for all but four apps.
Turn off cellular data usage for apps that don't need it
For iPhones and for iPads that have cellular service, you can limit what apps are able to use your cellular data - something that can avoid unnecessary drainage of both your data and battery when you are on the go.
Go to Settings → Cellular (or Mobile, Cellular Data, Mobile Data), found in the first section of Settings.
In the lower part of the screen you will see a list of the apps on your device that want to use Cellular Data. Turn off any that don't need internet access while you are on 3G/4G (ie they will then only work properly when you are on Wi-Fi).
If you don't need to use Cellular data at all, turn it off completely (first option in this settings screen) to conserve your battery.
Turn off Automatic Updates
In Settings → iTunes & App Store you will see a section called Automatic Downloads.
If any of the settings in this section are on, then updates to apps and/or content will happen automatically, regardless of whether your device is currently charging - something that could cause battery drain.
So turn this off if you want to avoid this. (You will then need manually do updates from the App Store app instead.)
If you don't want to waste your Cellular Data downloading updates to apps and other content (which can sometimes be very very large!), turn off Use Cellular Data.
Check what apps are tracking your location
Many apps on your device can use or need information about your location. In some cases, apps may be tracking your location even when you don't currently have the app open on your screen. This can be a battery drainer.
To see what apps are using you location, and turn off those that you don't really want doing this, go to Settings → Privacy → Location Services.
There is a switch at the top to turn off Location Services for all apps (which I would not do, given that I aways want to have 'Find My iPhone' active as a theft deterrent), and then switches for each app that uses Location Services.
In most cases you will be able to choose from one of two or three options.
While Using the App
Turn off iCloud Drive sync'ing over cellular
iCloud is able to use the internet to share data and photos between your iCloud-connected devices. But this is another area that utilises your battery (and your data).
To conserve both when you are not on Wi-Fi, disable use of Cellular Data for this sync'ing.
For iCloud Drive (if you have enabled this new feature), go to Settings → iCloud → iCloud Drive and, at the very bottom, slide the 'Use Cellular Data' switch to Off.
If you have not enabled iCloud Drive yet, this setting is in Settings → iCloud → Documents and Data.
Turn down your display's brightness
A big battery hog on your iPad and iPhone is the display - the brighter the screen, the more battery it consumes.
So turn down the brightness as much as you can. You can adjust the brightness from the Control Center.
Wwipe up from below the bottom of the screen to reveal the Control Center, and look for the brightness slider (indicated by 'suns' at either end).
A feature called Auto-Brightness can also consume a bit of battery, so can be turned off if you are trying to conserve power.
Turn off Wi-Fi and Bluetooth when not needed
Both Bluetooth and WiFi use a significant amount our battery, so can be turned off when not in use to conserve battery.
As for the previous tip, these features can be turned on and off from the Control Center - in the image here, the left symbol shows Wi-Fi is on (as it has a white background). Tap it to turn it off, making the background grey.
The same applies for the other symbol shown here for Bluetooth.
Turn off the movement of the screen (know as the 'parallax effect')
Have you noticed that, when you move your device around, the background seems to 'move' (and makes some people a bit dizzy!). This is a feature called the 'parallax effect' and, while it might seem like a great feature, it is also something that uses more battery than a 'still' background.
To turn this effect off, go to Settings → General → Accessibility → Reduce Motion
Make sure your device goes to sleep quickly when not in use
Make sure you have a feature called 'Autolock' turned on. Visit Settings → General → Autolock.
Autolock will put your device to sleep when you are not using it. When you turn it on, you nominate an autolock delay, which is the period after which your device will sleep when not in use. Set this to as short a period as possible.
Reset All Settings
Apparently, there may be a chance that crashes of system programs in background, caused by issues with an iOS 8 update, could be the culprit.
To rule this out, reset all settings. You will find this option in go to Settings → General → Reset (which is the last option in the General area).
This does not delete any apps or their data from your device. You Settings will just be set back to a 'default' state.
Any customisation your have previously applied to your Settings will have to be re-done, Wi-Fi passwords will have to be re-entered, you will need to sign back into iTunes, iCloud, iMessage, Facetime, etc.
The below articles, published over the past year or so, all cover the topic of how to conserve you device's battery life. You may find a few addtional tips that are worth trying, if you really need to conserve as much power as possible.