Problem with the S4

A

AC Question

So i had my S4 for approx. 1 year now but now its starting to act up. Everytime i lock my screen it disconnects from my wifi, it burns battery like crazy even tho im not using it and i stopped every app and as soon as i talk to someone on the phone it starts heating up to a point that it actually hurts my ear. I heard that some S4's had problems with the batteries so do i need a new battery or could it be a problem with the phone itself?

Thanks in advance