Visit an Apple Authorized Service Center and let them assess it for hardware problem.
There are several things to consider for battery draining issue with a device and it is not necessarily it is a hardware issue. A lot of iOS device users complains about the battery drain issue when updating to iOS 8.1 (specially on older devices).
Here are some tips that you can try to check which one cause for your battery to drain.
1. First, you'll want to figure out which apps are sucking away your battery life most. Apple has added a new tool in iOS 8 that gives a percentage breakdown of the biggest drainers. To identify which apps you should close when not in use, visit Settings > General > Usage > Battery Usage. You can then close out of these apps or just delete them, if they can be spared.
2. Just like with iOS 7, the latest Apple software comes with Background App Refresh set to "on." The feature lets apps run in the background while you multitask and continually refreshes content when running on Wi-Fi or a cellular network. It's handy for constant refreshing, but certainly not worth the battery life it drains along the way. To disable this feature, visit Settings > General > Background App Refresh. You can pick whether you want to turn off the function in general or via an app by app basis.
3. iOS 8 finally has widgets that you can access from Notification Center — just pull down from the top of the screen and customize your Today view. These widgets can offer up sports scores, weather updates, transit information and more. The only downside is that some of these widgets poll data frequently and that can be taxing on your battery. The good news is you can select which widgets you want to enable (and which ones you want to keep at bay) by tapping the "Edit" menu at the bottom of the Today screen.
4. Some people like how Apple's parallax feature makes it seem like the wallpaper can move behind the apps; others think it's dizzying. Either way, it's one of the biggest offenders of battery life for iOS 8. To turn it off, visit Settings > General > Accessibility and switch Reduce Motion to "on."
5. Location-tracking apps can be great for when you need GPS directions or even if you want to keep a geo-log of where you take your pictures, but the constant monitoring is eating away precious hours of device life constant monitoring is eating away precious hours of device life. You can turn off Location Services completely (Settings > Privacy > Location Services) or disable certain apps one by one. We recommend the latter option, so you can still leave on key location-based functions such as Find My iPhone if it's ever lost. There's more, too. Selecting the System Services option under Location Services will reveal a collection of other app features that are stealing away battery life, including "Popular Near Me" and "Frequent Locations."
6. This may seem obvious, but your display is draining your battery, and there's no need to have it shine any brighter than necessary. Use the Control Center or visit Settings > Wallpapers & Brightness and disable Auto-Brightness and decrease the setting manually.
7. We understand the constant need to be connected and not miss emails, but the fetch function — which pushes email notifications to your homescreen — is always looking for new mail and exhausts the battery along the way. Give it a rest and check your email manually via the Mail app instead. To turn off the feature, visit Settings > Mail, Contacts, Calendars > Fetch New Data.
8. Also, you might want to disable LTE as this also cause for the battery to drain specially if there are no LTE coverage within the area.
Common problem with iPhone (I should know) XD Check if you dont have running apps (double press the home button), if even in standby mode the battery is always used up, have it checked. Good Day.
If you're still under warranty, visit an Apple authorized service center and have it checked.
The iPhone 5 series usually have this "battery" problem. If you're not covered by the Apple warranty anymore, you can always proceed to Greenhills and have your battery replaced there. Hehe