If you leave your iPhone plugged in to an outlet or computer all night (presumably charging), you may notice in the morning that your iPhone is only charged up to around 92-93%. This is a common problem and is a result of your iPhone's battery's calibration. To fix this, follow the steps below:
Step 1) Restart your iPhone by holding down the home button and the sleep/wake button at the same time.
Step 2) Use the phone until the battery runs down to 0% and shuts itself off. Then charge it all the way up to 100%. This will calibrate the battery, but only do this about once a month.
Step 3) When the charging icon changes to fully charged and it is not at 100% yet, simply unplugging the device and then replugging it in will allow it to charge up to 100%.
Step 4) Restore your iPhone using this guide here.
Step 5) Finally, sometimes with new hardware, it takes a few days/weeks to correctly calibrate the battery. You should notice that after a few weeks, the battery readouts will be more accurate and be charged fully up to 100%.