Why power very fast loosing?

@badrulhish29324 there are many reasons that can be responsible for this. First you want to make sure that you use power -saver settings. This should work for your phone:

Slide two fingers downwards starting from the top of the screen. Press Battery saver to turn on the function. Press the Home key to return to the home screen.

If that does not accomplish anything, I would suggest you replace the battery. A depleted battery will tell you it charged to 100% but does no longer have the capacity it did when new. Replace the battery and re-evaluate.

Since iFixit does not yet have a specific guide for this, use something like this video Replacement batteries are readily available at many online stores.

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!