iPhone 4s became hot quickly draining battery and shutdown unexpectedly I have iPhone 4s and it becomes slowly day by day so I decided reset (format) my phone and reset it as a new iPhone. Then I began to install my essential apps. It's comes to know that my iPhone got unexpectedly shutdown, while making a call, during the conversation with messenger or regular phone call. The iPhone also getting very hot and battery draining very quickly. 
It was in rather good condition except slow. To make it fast I'm facing this problem. Please help me if there are any remedy?

It's running with iOS Version: 9.3.5 ( 13G36 )
It sounds like a battery issue.

You may need to take it to a repair shop and have it replaced IMMEDIATELY. 

I say that because I have seen an iPhone 4 battery explode before. It's not a pretty sight. Consider the average lifespan of a lithium battery: 


  The typical estimated life of a Lithium-Ion battery is about two to
  three years or 300 to 500 charge cycles, whichever occurs first.


This is a very common issue for the iPhone 4 and can be repaired pretty easily. 

I'm also going to cite my personal and proffesional experience with this.