iPhone 4s turns itself off It started today and happened twice, my iPhone turns itself off even battery has 15%-17% charge, I can't open it, empty battery sign appears when I plug it in to charge, it begins to charge from 15%-17%, I couldn't find the reason, it has the latest iOS update, what could it be?
The clue is that it begins to charge at 15% or so.. you have some bad cells in the battery, so they are not considered for charging, but are part of the 100% the battery should have.

Take it in to Apple and have them look at it!