There are no apps running in the background (I recently factory reset it, no third party apps have been installed except one or two; and I am sure they are not the ones draining battery) and I have tried replacing the battery too; but the drain is 5℅ per hour when the phone is idle. The network signal is strong all time. I have never faced such issues earlier.
The phone is around 2 years old and the new battery is 3 days old. The new battery is genuine. Even the older battery (genuine) is perfectly alright, I know that.
Every app that I use drains up lot of battery, say for instance I use Calculator for 5 minutes, Whatsapp for 2 minutes (making sure that after using they do not keep running in the background) and Chrome browser for 5 minutes, battery drain will be: for Calculator 25%, Whatsapp 20%, Chrome 30℅. What could be the reason for such an issue?