@priyamdutta sounds like a bad battery. Replace the battery and then reevaluate. Since iFixit does not yet have a specific guide for that, use something like [https://www.youtube.com/watch?app=desktop&v=y0t76eOW878|this video] to change the battery.
While you work on your phone, take lots of pictures. Once you are done with it, take those pictures and create a guide for iFixit. That will help the next person that has a device with the same issues as you do. It's easy and fun to create these guides. https://ifixit.com/Guide/new The iFixit community will appreciate this.
Repair is War on Entropy!