If nothing positive comes out of a battery calibration, or if you can't do it at all, the last troubleshooting step is to update the phone through DFU Mode. It's essentially a factory reset, but with the assistance of a computer. Follow these steps to accomplish it:

1. Close all active apps on your 
2. Launch iTunes.
3. Turn your iPhone off. If you can't switch it off properly, deplete the battery to 0% and the phone will shut down on its own. Without attempting to turn it on, charge the phone for at least one hour.
4. Use a USB cord to connect your iPhone to your computer.
5. For at least 3 seconds, press and hold the Power button.
6. While holding the Power button, press and hold the Volume Down button on the left side of the iPhone. Make careful you turn off both the power and the  If Apple logo appears at this time, repeat steps 5 and 6. Apple logo should not show at all.
7. Hold the Volume Down key down for another 5 seconds. Repeat steps 5-7 if the Plug into iTunes screen appears. The screen that appears when you plug in your device to iTunes should not appear.
8. If the screen on your phone remains dark, you're in DFU mode. After that, your computer should inform you that an iPhone has been discovered by iTunes.
9. To complete a full recovery, follow the on-screen instructions on your iPhone 7