Why dose my device heats up while charging?

So my iPhone resently gets this problem when I plug it in to charge it gets really hot near the dock connector flex cable. My hypothesis is that the dock connector might be damaged and am willing to replace it but I am not quite sure because it could also be a batterie problem. I just want to check with you guys so I don't waste money on buying the wroung part please help me guys I have gotten other problems and you guys seemed to really help me out so thanks and good night everyone ;).