Why my charge drain fast

@gurungprince make sure that you have set your phone to battery savings as well as turn all background Apps off. You have to make sure that it is not the software or the settings that deplete the power. If all of those settings are properly set, and the battery still drains fast, it will be time to replace the battery.

Since iFixit does not yet have a guide for this, use something like this video to work on it.

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 the same issues with their device. 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!