Calculate phone's battery capacity

I am basing this answer on the concerns expressed in comments and your main question

• Firstly, there are many ways of measuring mAH of batteries with different results, so the device manufacturer is the best person to ask this question- it claims to read battery capacity but how it measures is not known from the product description. There are different methods for hardware measurements with varying results ( a subject in itself ). See this to get a feel

How to measure capacity of a Lithium-ion battery - Electrical Engineering Stack Exchange

• Next, as covered in the answer here
  Where are the battery capacity files located?, it is quite possible to amend the values on a rooted device but ultimately it depends on the app which chooses from where to read the values from




• Your main concern, it appears to me is to know the true mAh of battery which is covered here using the 3C app , in my answer How to determine maximum capacity of a battery in mAh? - received fake battery