iphone 5 go off battery 20%
I have an iPhone 5 bought in novembre of 2012. i notice that the battery go off so quickly, but this is normal in this king of phone, you are using all the time. But i dont understan when my iphone have the 20% of the battery and turn off, i wait for a 1 minute and try to turn on, it begin to start the iphone, but when i going to enter the pin code the phone with the 20% of the battery turn off again. I have to plug the charger and i can use again.
This it not always, but every day is going worse, before it turned off with 10-15%, now it turned off with the 20%.
I live in seville (Spain), where can i go to get help.
Thank you.
iPhone 5, iOS 7.0.3