Can you calibrate the battery of iPhone? It seems strange. But you can, at least, calibrate telephone monitoring and report the percentage of remaining battery power. This is the case when iPhone begins to provide inaccurate percentages. Either it lasts for an hour and a half or longer to show a low percentage at the end, or it shows a steady battery charge and then suddenly shuts down. Discharge the battery completely and drain the battery until it turns off. You can open more applications to speed up power consumption, such as using flashlights or videos. Let the phone discharge and unplug the power plug to ensure that the battery is completely depleted. Although the phone is still powered off, it takes hours longer to charge it to "100%" capacity. Restart the phone and then perform soft reset (also known as thermal reset). Different iPhone models have different soft reset methods For models earlier than the iPhone 7 (e.g. the iPhone SE, 6S, 6, 5S, 5, 4S, 4), you must press the Sleep / Wake button and the Home Page button simultaneously for about 10 seconds. If your phone is the iPhones 7 or 7 Plus, you have to press the volume down button and the sleep / wake up button again for about 10 seconds. For the iPhone X, 8, and 8 Plus, you have to press and release the volume up button, then press and release the volume down button, and finally hold the side button until the Apple logo appears.