I'm using MI 4 model, I'm bought a mobile in two yrs before. I'm having an one issue, recent two days my mobile got battery drained so fast, tell me the reason.. I'm also used factory reset method but, there is no use of it.pls tell me the solution for the issue.

My phone model redmi note 6 pro... I what to change my battery....i what to know the Price to change the battery