Every now and then my Ipad and Iphone battery needs refreshing.
This observation is from my own experience.
Take note that both devices are used intensively.
Iphone 4s with IOS Version 5.1.1
Owned since 2011 but battery was replaced in 2013 cause it was damaged due to heavy gaming while charging.
Ipad 4 with IOS Version 6.1.3
Owned since 2013
I was always charging them while turned ON but I do not use them while charging them anymore.
Firstly I was starting to notice that as soon as I unplugged the charger and after about 1 minute of use the battery meter showed 97%.
The Iphone starts to shut down usually when the battery meter is at 20%.
The Ipad shuts down at 3% to 7%, Yes I always try to use the most of my battery.
Plug the charger while the device is ON.
Make sure the device is being charged.
Turn off the device.
If you turn off the device first, it will turn ON automatically.
For any questions feel free to comment.