You have to calibrate your battery every once in a while. I do calibrate my Mac every month pero depende rana nimo. This goes to iPhone, iPad, or MACs. Battery indication tends to offset through time and sometimes indicates falsely.
Check this out....
HOW TO CALIBRATE APPLE PRODUCTS BATTERY
Basically here are the steps. Also, it's better to read the link above for more info.
Step One:
Use the device until the battery has drained to the point of self-shutdown. Basically, use it until it turns itself off.
Step Two:
Recharge the battery without any interruptions until it is fully charged to 100%.
(The device will automatically turn "ON" once it gains enough battery power)
Step Three:
For mobile devices such as iPhones, iPads, or iPod Touches, reset the device by holding the Sleep/Wake button at the top and the Home button at the bottom until you see the Apple logo then release. You can ignore the “Swipe to Power Off” option.
Again, hold down the Sleep/Wake button and Home button all at the same time while your device is ON. Just continue even the "Swipe to Power Off" will appear, the device will shut down then the apple logo appears. That's the time you will release both buttons.
TIPS ON HOW TO EXTEND BATTERY LIFE
HOPE THIS HELPS