my iphone went dead with over 50% power
my iphone 4s went dead overnight with over 50% power. it could not turn on in the morning!
iPhone 4S, iOS 8.0.2
Did you already try to reset the phone by holding the sleep and home button for about 10sec, until the Apple logo comes back?
If this does not help, get your phone checked by visiting an Authorized Apple Service Provider or Apple Store next to your place.
You can also contact Apple Support and ask them to service the phone. Depending on the age and use of the phone, your battery might have died and needs to be replaced.
You can also visit this page to do that: iPhone - Contact Support - Apple Support
Click on Apple Support, then on ->Battery, Power &Charging ->Battery questions and troubleshooting, and follow the instructions.