Battery display is not working

@musawaheed that percentage gets reported via the "Gas Gauge" connection. For now, I suggest you replace the battery. Anything after that is either related to an issues with the circuitry on your motherboard or with the software. You can alway try to restore your software by doing a factory reset, but you will lose all of your files (pictures/contacts/SMS/music etc.) so you will need to make sure that you have a backup of those.

Something like this video will at least get you to the battery. Using an opening pick would most likely make this an easier job.

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!