Check Battery Level iOS Swift

Xcode 11 • Swift 5.1

First just enable battery monitoring:

UIDevice.current.isBatteryMonitoringEnabled = true

Then you can create a computed property to return the battery level:

Battery level ranges from 0.0 (fully discharged) to 1.0 (100% charged). Before accessing this property, ensure that battery monitoring is enabled. If battery monitoring is not enabled, battery state is UIDevice.BatteryState.unknown and the value of this property is –1.0.

var batteryLevel: Float { UIDevice.current.batteryLevel }

To monitor your device battery level you can add an observer for the UIDevice.batteryLevelDidChangeNotification:

NotificationCenter.default.addObserver(self, selector: #selector(batteryLevelDidChange), name: UIDevice.batteryLevelDidChangeNotification, object: nil)

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Battery level ranges from 0.0 (fully discharged) to 1.0 (100% charged). Before accessing this property, ensure that battery monitoring is enabled.
If battery monitoring is not enabled, battery state is UIDevice.BatteryState.unknown and the value of this property is –1.0.

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@objc func batteryLevelDidChange(_ notification: Notification) {
    print(batteryLevel)
}

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You can also verify the battery state:

var batteryState: UIDevice.BatteryState { UIDevice.current.batteryState }

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case .unknown   //  "The battery state for the device cannot be determined."
case .unplugged //  "The device is not plugged into power; the battery is discharging"
case .charging  //  "The device is plugged into power and the battery is less than 100% charged."
case .full      //   "The device is plugged into power and the battery is 100% charged."

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and add an observer for UIDevice.batteryStateDidChangeNotification:

NotificationCenter.default.addObserver(self, selector: #selector(batteryStateDidChange), name: UIDevice.batteryStateDidChangeNotification, object: nil)

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@objc func batteryStateDidChange(_ notification: Notification) {
    switch batteryState {
    case .unplugged, .unknown:
        print("not charging")
    case .charging, .full:
        print("charging or full")
    }
}