I bought my S4 exactly a yr ago... it worked fine until christmas.. then my phone's battery started heating up .. initially i thought might b due to gaming.. but noo, as a month passed by the heating got worse.. couldnt keep the phone in my pocket.. battery temp wewnt upto 44 degrees.. which isnt normal even during normal use like fb, twitter.. samsiung service even looked into the matter and gave me a replacement battery.. but even that didnt do much help.. ! might b a kitkat problem..god knws!