UIDeviceListener is an Objective-C class that retrieves device power information for iOS devices, including battery health information, charging information, etc. The magic is that this is done without relying on any private APIs. UIDeviceListener is extremely easy to use and runs well on all recent versions of iOS.

UIDeviceListener retrieves raw data from the system regarding battery capacity, cycle count, state of charge, and much much more. UIDeviceListener also presents detailed information regarding the currently plugged in power adapter. None of this is currently (as of iOS 9) available in any public API.

NOTE: As of iOS 10 beta 1, it appears that Apple has removed nearly all power information from this dictionary, and there doesn't appear to be any way to retrieve this information. The information appears to have been removed from IOKit.

The information provided by UIDeviceListener is available in the IORegistry and could be gathered relatively easily by directly calling IOKit. Unfortunately, IOKit is considered a private framework and so using it almost guarantees that your app would be rejected by Apple's App Review team if you were to submit it to the App Store. UIDeviceListener doesn't use IOKit, neither directly nor indirectly. UIDeviceListener also doesn't rely on any other private API. Please see the How it works section below to learn more.

Using UIDeviceListener is quite simple. First, copy the source files (UIDeviceListener.h and UIDeviceListener.mm) to your project. Then, import UIDeviceListener.h into your source file and initialize the listener as follows:

    UIDeviceListener *listener = [UIDeviceListener sharedUIDeviceListener];
    
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(listenerDataUpdated:) name: kUIDeviceListenerNewDataNotification object:nil];
    
    [listener startListener];

Then, in your observer callback:

- (void) listenerDataUpdated: (NSNotification *) notification
{
    NSDictionary *powerDataDictionary = notification.userInfo;
    // Use your power data here!
}

That's all there is to it. You will receive the first notification when you first call startListener and then afterwards periodically, as the power data is updated. On most devices this happens every 20 seconds or so, but it also happens in real-time as the device is plugged in and out. See below for a sample of the kind of data contained in the dictionary, or just run the sample program on your device to see how the dictionary refreshes and what it contains.

Alternatively, you can use EEPowerInformation and not even worry about UIDeviceListener. EEPowerInformation is an abstracted power information class that uses UIDeviceListener to obtain the information, chews it up, makes up for any iOS differences, and exposes pretty properties with all of the pertinent data. To use, simply initialize as follows:

    powerInformation = [[EEPowerInformation alloc] init];
    powerInformation.delegate = self;

Then, listen to the delegate callback as follows:

- (void) powerInformationUpdated: (EEPowerInformation *) powerInfo
{
    NSLog(@"Battery cycle count: %ld", powerInfo.batteryCycleCount);
}

EEPowerInformation adds a number of convenience methods that might save you some time figuring out what each property means. EEPowerInformation is extensively documented in EEPowerInformation.h.

Go ahead, but you're still likely to get rejected by Apple. Even though UIDeviceListener is likely going to pass any technical tests Apple runs on your App, the App Review team consists of human beings who are likely to detect that your app presents information that Apple doesn't deem "end-user appropriate"... The most likely outcome is your app getting rejected under section 2.19 of the App Review Guidelines:

2.19 Apps that provide incorrect diagnostic or other inaccurate device data will be rejected

Of course, the data presented is about as accurate as it could ever be, but clearly Apple has decided that for now they're not willing to present this data to end-users, and so expect to get this rejection. Still, UIDeviceListener can be useful for apps where the data obtained is not directly presented to the end-user.

Pretty much every datapoint regarding battery and power known to the system is exposed. This includes the following:

• Battery design capacity
• Battery current raw capacity (in mAh)
• Battery cycle count
• Current battery temperature
• Current battery voltage
• Current battery discharge rate (device power consumption), in mA

Additionally, when the device is plugged in there is rich information regarding the currently plugged in power source:

• The wattage and amperage of the currently plugged in adapter. This will even detect the new 29W USB-C adapter that's supported by the 12.9" iPad Pro.
• The actual battery charging rate (in mA), if the device is charging
• Confirmation that the device is actually charging. On some power hungry iOS devices you will often see devices consuming some battery power even though they are plugged in.

Here is a sample dictionary showing actual output from UIDeviceListener. Unfortunately the dictionaries have slight differences for different versions of iOS. Certain basic parameters are identical across all versions, but there are bits of data that are quite different across versions. Still, basics such as AdapterDetails, AppleRawCurrentCapacity, AppleRawMaxCapacity, and CycleCount are identical across all supported versions (so far tested iOS 7 through 9.3.1).

{
    AdapterDetails =     {
        Amperage = 1000;
        Description = "usb host";
        FamilyCode = "-536854528";
        PMUConfiguration = 1000;
        Watts = 5;
    };
    AdapterInfo = 16384;
    Amperage = 1000;
    AppleRawCurrentCapacity = 1279;
    AppleRawMaxCapacity = 1275;
    AtCriticalLevel = 0;
    AtWarnLevel = 0;
    BatteryData =     {
        BatterySerialNumber = REDACTED;
        ChemID = 355;
        CycleCount = 524;
        DesignCapacity = 1420;
        Flags = 640;
        FullAvailableCapacity = 1325;
        ManufactureDate = REDACTED;
        MaxCapacity = 1273;
        MfgData = REDACTED;
        QmaxCell0 = 1350;
        StateOfCharge = 100;
        Voltage = 4194;
    };
    BatteryInstalled = 1;
    BatteryKey = "0003-default";
    BootBBCapacity = 52;
    BootCapacityEstimate = 2;
    BootVoltage = 3518;
    CFBundleIdentifier = "com.apple.driver.AppleD1815PMU";
    ChargerConfiguration = 990;
    CurrentCapacity = 1275;
    CycleCount = 524;
    DesignCapacity = 1420;
    ExternalChargeCapable = 1;
    ExternalConnected = 1;
    FullyCharged = 1;
    IOClass = AppleD1815PMUPowerSource;
    IOFunctionParent64000000 = <>;
    IOGeneralInterest = "IOCommand is not serializable";
    IOInterruptControllers =     (
        IOInterruptController34000000,
        IOInterruptController34000000,
        IOInterruptController34000000,
        IOInterruptController34000000
    );
    IOInterruptSpecifiers =     (
        <03000000>,
        <26000000>,
        <04000000>,
        <24000000>
    );
    IOMatchCategory = AppleD1815PMUPowerSource;
    IOPowerManagement =     {
        CurrentPowerState = 2;
        DevicePowerState = 2;
        MaxPowerState = 2;
    };
    IOProbeScore = 0;
    IOProviderClass = AppleD1815PMU;
    InstantAmperage = 0;
    IsCharging = 0;
    Location = 0;
    Manufacturer = A;
    MaxCapacity = 1275;
    Model = "0003-A";
    Serial = REDACTED;
    Temperature = 2590;
    TimeRemaining = 0;
    UpdateTime = 1461830702;
    Voltage = 4182;
    "battery-data" =     {
        "0003-default" = <...>;
        "0004-default" = <...>;
        "0005-default" = <...};
    "built-in" = 1;
}

UIDeviceListener has been extensively tested and runs well on essentially any iOS device (iPod Touch, iPad, and iPhone). UIDeviceListener supports iOS 7 and later, with 9.3.1 being the most recent version that's been tested.

UIDeviceListener essentially hijacks the power data from iOS. We use UIDevice, which is a public API for getting system information. Internally, UIDevice utilizes IOKit (and the specific power dictionary we're after) in order to get information for two specific properties: batteryLevel and batteryState.

UIDeviceListener relies on a CoreFoundation feature called CFAllocator, whereby apps are allowed to replace the default allocator for a given thread. We replace the default allocator with our own. That allows us to keep track of allocations being made on this one thread, at a very specific point in time (see below). This allows us to capture CF allocations made by anyone (including system components), and then examine those allocations, looking for our specific object.

After it replaces the default allocator, UIDeviceListener tells UIDevice to listen for updates to the batteryLevel and batteryState properties (it does so by setting the batteryMonitoringEnabled property to YES).

As updates come in on those two properties, the default CF allocator traps all CF objects created by UIDevice. Then, we configure UIDevice to notify us whenever new values have been set for batteryLevel and batteryState (we do that by installing a Key-Value Observer (KVO) on those two properties). In the KVO, we scan our default allocator's data structure, looking for our particular CFDictionary. Because UIDevice is still holding a reference to our desired CFDictionary while it sets the value of the properties, we are able to hijack that dictionary and get to the data.

This is obviously a hack. The approach works perfectly on iOS 7 through iOS 9.3.1, but that does not guarantee that future iOS updates won't break it. It relies on a number of implementation details in UIDevice that are definitely subject to change by Apple without warning. In that sense using this library is equivalent to using a private API, so consider yourself warned...