Why is my iPhone battery draining slower?

For a week I had my battery drain from 100 percent down to 6 percent in 15 minutes.
I reset my phone to resemble a new iPhone and it goes from 100 percent to 60 percent in 2 hours. Why is this?

Happens to almost everybodys phone at some point. Try this and see if helps 1. Go to Settings on your phone 2. Go to General 3. Tap on Reset 4. Choose Reset All Settings 5. If have Passcode enter it 6. Confirm the Reset 7. Once again Confirm--Hope this helps

A few questions

what model of iphone
which ios are you running