Develop Reference

How to programmatically connect to wifi in Android

I've been searching on this for quite some time, and have found lots of solutions that ultimately use the Android GUI to prompt the end-user for connection/confirmation. We would like to present a user with a form and directly connect to the specified network. I understand from a security perspective why this is necessary, but in our case, it is a system app going on a fully managed Android device. It is not intended for general use in the Play store. We are using Xamarin, but I can adapt any Java/Kotlin code.
The closest I've found thus far is the following (using C#):
public void ConnectToWifi(string ssid, string password = "") {
var wifiNetworkSpecifier = new WifiNetworkSpecifier.Builder().SetSsid(ssid);
if (!string.IsNullOrEmpty(password))
wifiNetworkSpecifier.SetWpa2Passphrase(password);
var networkRequest = new NetworkRequest.Builder().AddTransportType(TransportType.Wifi)?
.SetNetworkSpecifier(wifiNetworkSpecifier.Build())?.Build();
if (networkRequest is null)
return;
var theNetworkCallback = new TheNetworkCallback();
var connectivityManager = (ConnectivityManager?)MainActivity.Current.ApplicationContext?
.GetSystemService(Context.ConnectivityService);
connectivityManager?.RequestNetwork(networkRequest, theNetworkCallback);
}
It sorta works, but does prompt the end-user, and my understanding, this approach is deprecated and doesn't work well in newer versions of Android. We're hoping for a solution that works in Android 11.
I'm even fine if there's a solution to write directly to wifi files on the OS. I've seen various solutions to manually populate entries via ADB, but I'm having a tough time adapting that to Xamarin/Java (can't seem to access the /data/misc/wifi directories). Again, this is intended for use exclusively on our own managed devices.

I have a blog post about this topic here: https://blog.ostebaronen.dk/2020/11/android-11-wifi.html
Android Network API is not the greatest thing to work with as there are pitfals depending on the API level the code runs on.
From Android 10 and up a lot of the Network stuff has been restricted for "privacy" reasons, so you cannot work around not asking the user for input, unless the device is rooted or your App is set up as Device Admin.
For Android 11, there is a new API to present a system dialog and allow the user to save and connect to a network. This will look something like:
You can launch this through an Intent called android.settings.WIFI_ADD_NETWORKS:
var intent = new Intent(
"android.settings.WIFI_ADD_NETWORKS");
var bundle = new Bundle();
bundle.PutParcelableArrayList(
"android.provider.extra.WIFI_NETWORK_LIST",
new List<IParcelable>
{
new WifiNetworkSuggestion.Builder()
.SetSsid(ssid)
.SetWpa2Passphrase(password)
.Build()
});
intent.PutExtras(bundle);
StartActivityForResult(intent, AddWifiSettingsRequestCode);
You can then get the result in your Activity overriding OnActivityResult and fetching the result like so:
if (requestCode == AddWifiSettingsRequestCode)
{
if (data != null && data.HasExtra(
"android.provider.extra.WIFI_NETWORK_RESULT_LIST"))
{
var extras =
data.GetIntegerArrayListExtra(
"android.provider.extra.WIFI_NETWORK_RESULT_LIST")
?.Select(i => i.IntValue()).ToArray() ?? new int[0];
if (extras.Length > 0)
{
var ok = extras
.Select(GetResultFromCode)
.All(r => r == Result.Ok);
// if ok is true, BINGO!
return;
}
}
}
I have a repository here with the full sample: https://github.com/Cheesebaron/Android11WiFi
From using this in the wild, I've found that this API does not work nicely with some OEMs such as OnePlus and Huawei. Some of these either restrict or the System Settings App simply crashes due to a misconfiguration on their part. For those I fall back to the API's introduced in Android 10.

Is the Android Wifi-API really so broken on Android 10+?

I'm working on a Wifi auto connect feature and I am shocked how broken that API is.
I'm using now 5 different APIs and I still don't get it in a way the user would expect it.
I have a setting to enable wifi auto connection on Android 10+ I'll try this:
Check if I hold the ACCESS_WIFI_STATE permission with:
appOpsManager.unsafeCheckOp("android:change_wifi_state", Process.myUid(), context.packageName) == AppOpsManager.MODE_ALLOWED
When I own the permission I go on with 2. if not I continue with 6.
When I hold the permission I'll check on Android 11+ if from a previous run my wifi suggestion was saved wifiManager.networkSuggestions.isNotEmpty() if that is true I check which Wifi I'm currently connected with see step x. On lower levels I skip this and go to step 3
I use the wifi suggestion API with the WifiNetworkSuggestion.Builder() and suggest the user my wifi with
val status = wifiManager.addNetworkSuggestions(listOf(suggestion))
// Strage bug: On first usage the return value is always SUCCESS
val success = status == WifiManager.STATUS_NETWORK_SUGGESTIONS_SUCCESS
When the user accepts my suggestion I'm fine so far. I cannot verify on Android 10 if my suggestion was accepted. On Android 11 this is possible (see step 2). However I still don't know if the device actually connected with the wifi. So I go to step 7
When the user rejected my suggestion I'm almost out of the game I can never ask the user again (well technically there is a well hidden feature where you can switch the permission, but no user will ever find it). On Android 10 I can just check if I'm connected with the right wifi, well at least theoretically (see step 7).
On Android 11+ I can fallback to the Settings.ACTION_WIFI_ADD_NETWORKS intent which can always add Wifis (with the downside that the user can share the wifi password)
I need to verify if the steps before worked and the user is actually connected to the desired wifi. To do so I already own the permissions ACCESS_WIFI_STATE, ACCESS_NETWORK_STATE, ACCESS_COARSE_LOCATION and ACCESS_FINE_LOCATION. However the ConnectivityManager API don't return the actual SSID, that drives me crazy.
If the user is not connected to the right wifi I would try to use the Settings.Panel.ACTION_WIFI action to let the user to connect to the right wifi
To summarize that:
I use the WifiNetworkSuggestion API
I fallback to Settings.ACTION_WIFI_ADD_NETWORKS where possible
I try to verify if the user is currently connected to the right wifi
I try to assist the user to conenct to the right wifi (or even turn wifi on) with the Settings.Panel.ACTION_WIFI action
Is that really such a mess or is there a easier way?
I'm currently accessing the SSID like this:
private val currentSsid: String?
get() =
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q) {
val wifiInfo = connectivityManager.getNetworkCapabilities(connectivityManager.activeNetwork)?.transportInfo as? WifiInfo
wifiInfo?.ssid
} else {
wifiManager.connectionInfo?.ssid
}
Based on Unable to get WIFI SSID using onCapabilitiesChanged in Android 12 I think that way I access the value is not supported. I get currently the value "<unknown ssid>".

Well just a half answer, but it might help anyway. Here is how I get the current SSID of the user (you need to hold the location permission):
fun updateSsid(networkCapabilities: NetworkCapabilities) {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q) {
currentSsid = (networkCapabilities.transportInfo as? WifiInfo)?.ssid?.trim('"')
}
}
wifiCallback = when {
Build.VERSION.SDK_INT >= Build.VERSION_CODES.S -> {
object: ConnectivityManager.NetworkCallback(FLAG_INCLUDE_LOCATION_INFO) {
override fun onCapabilitiesChanged(network: Network, networkCapabilities: NetworkCapabilities) {
updateSsid(networkCapabilities)
}
}
}
Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q -> {
object: ConnectivityManager.NetworkCallback() {
override fun onCapabilitiesChanged(network: Network, networkCapabilities: NetworkCapabilities) {
updateSsid(networkCapabilities)
}
}
}
else -> null
}
wifiCallback?.let {
fragment.lifecycle.addObserver(object: DefaultLifecycleObserver {
override fun onResume(owner: LifecycleOwner) {
connectivityManager.registerNetworkCallback(request, it)
}
override fun onPause(owner: LifecycleOwner) {
connectivityManager.unregisterNetworkCallback(it)
}
})
}
So basically aspects of your code need to check apis for the levels <10, 10, 11 and 12. What a mess.
This might be quiet handy if you want the user to pick the configured wifi:
fun showWifiDialog() {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q) {
try {
fragment.startActivity(Intent(android.provider.Settings.Panel.ACTION_WIFI))
} catch (e: Exception) {
// ignored
}
}
}

Is it possible to add a network configuration on Android Q?

Background
I've noticed that in WifiManager class there is a function called addNetwork, that might be useful if I want to restore or save networks information (network name AKA SSID, together with the password and the type), so that I could also connect to it.
The problem
I can't find much information about how to do such a thing. I've seen various examples on StackOverflow, and if I target Android API 28 (or below), I indeed succeed to make it add a network and even connect to it.
When targeting Android 29 (Android Q), however, it fails to add the network.
What I've found
Since I'm trying on Pixel 2 with Android Q beta 4, I think that maybe it's because addNetwork is deprecated, so the docs even say so, and that if I target Android Q, it won't work, and indeed it doesn't work:
Compatibility Note: For applications targeting Build.VERSION_CODES.Q
or above, this API will always return -1.
The way it seems it should work up till Android Q (excluding), is by preparing WifiConfiguration and adding it. Later I can also connect to it if I wish. On Android Q, it seems it was replaced by WifiNetworkSuggestion, but it doesn't seem like it's about adding a network at all:
The Network Suggestion object is used to provide a Wi-Fi network for
consideration when auto-connecting to networks. Apps cannot directly
create this object, they must use
WifiNetworkSuggestion.Builder#build() to obtain an instance of this
object.
Apps can provide a list of such networks to the platform using
WifiManager#addNetworkSuggestions(List).
Here's my current code, for pre-Android-Q
#WorkerThread
fun addNetwork(context: Context, networkName: String, networkPassword: String? = null, keyMgmt: Int = WifiConfiguration.KeyMgmt.NONE) {
val wifiManager = context.getSystemService(Context.WIFI_SERVICE) as WifiManager
val conf = WifiConfiguration()
conf.SSID = "\"$networkName\""
conf.preSharedKey = if (networkPassword.isNullOrEmpty()) "" else "\"$networkPassword\""
conf.allowedKeyManagement.set(keyMgmt)
when (keyMgmt) {
WifiConfiguration.KeyMgmt.WPA_PSK -> {
//WPA/WPA2
}
WifiConfiguration.KeyMgmt.IEEE8021X -> {
}
WifiConfiguration.KeyMgmt.WPA_EAP -> {
}
WifiConfiguration.KeyMgmt.NONE -> {
if (networkPassword.isNullOrEmpty()) {
//open network
conf.wepKeys[0] = "\"\""
} else {
//wep
conf.wepKeys[0] = "\"" + networkPassword + "\""
conf.wepTxKeyIndex = 0
conf.allowedGroupCiphers.set(WifiConfiguration.GroupCipher.WEP40)
}
}
}
if (networkPassword.isNullOrEmpty()) {
//open network
conf.allowedKeyManagement.set(WifiConfiguration.KeyMgmt.NONE)
} else {
}
wifiManager.isWifiEnabled = true
while (!wifiManager.pingSupplicant()) {
Log.d("AppLog", "waiting to be able to add network")
}
val networkId = wifiManager.addNetwork(conf)
if (networkId == -1)
Log.d("AppLog", "failed to add network")
else {
wifiManager.enableNetwork(networkId, false)
Log.d("AppLog", "success to add network")
}
}
Seems it requires only these permissions:
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE"/>
<uses-permission android:name="android.permission.CHANGE_WIFI_STATE"/>
But in any case, this works as long as you don't target Android Q (API 29) and above. When you target it, I indeed always get "-1" as a result, meaning it fails.
I've also found an issue on the issue tracker (here and I wrote about it here), telling about someone that needs the API back, but I'm not sure it's about adding a network.
Looking at WifiNetworkSuggestion, I don't see that it has as many things to set as WifiConfiguration via its builder, so this is another reason for why I suspect it's not about adding a network.
But I tried anyway. Here's the code I've tried, for example, to add a normal WPA network:
#WorkerThread
fun addNetworkAndroidQ(context: Context, networkName: String, networkPassword: String? = null) {
val wifiManager = context.getSystemService(Context.WIFI_SERVICE) as WifiManager
val list = ArrayList<WifiNetworkSuggestion>()
val builder = WifiNetworkSuggestion.Builder().setSsid(networkName)
if (!networkPassword.isNullOrEmpty())
builder.setWpa2Passphrase(networkPassword)
list.add(builder.build())
val result = wifiManager.addNetworkSuggestions(list)
if (result == WifiManager.STATUS_NETWORK_SUGGESTIONS_SUCCESS)
Log.d("AppLog", "success")
else Log.d("AppLog", "failed")
}
When running (I gave it my Wifi network details, after making the OS forget about it), it says it succeeded, but nothing occurred on the OS's Wifi settings. The network doesn't exist there with the password I've added. So I really don't get what it did...
After a few long seconds, I've noticed a notification asking me if it's ok to connect to the suggested networks made by the app:
But still when I chose that I accept, it didn't do anything, as before.
I tried to make another POC, thinking I might have done it incorrectly, but then it didn't even show the notification. Since I think this whole behavior is a bug, I've reported about it here.
Not only that, but I've found out that if indeed it is supposed to add a network one way or another, it still has some serious restrictions, such as max added networks (here) and being removed upon uninstall of the app (here)
The questions
How should Android Q be handled exactly? Is there really no API anymore to add a network?
If WifiNetworkSuggestion is not about adding a network, what is it really used for exactly?
Since I'm not familiar enough with the tidbits of adding a network, is my code correct about all possible ways to add a network? I ask this because someone wrote here that people should enable Wifi and make sure pingSupplicant returns true. Is it true? Or would it be enough to just call addNetwork ?
If it's now impossible to add a network using the normal API, is there maybe a solution by using a rooted device instead? Maybe some adb command?
EDIT: Not sure how to do it officially, but using adb, you might be able to add Wifi-networks on Android 11 . Need to check adb shell cmd wifi help .

I stuck with same issue, but somehow I reached a reproducible state for connecting a desired network and I want to share my findings it may helps.
As a summary:
You have to disable all auto connection before applying WifiNetworkSuggestion logic
For more details, Please read the following:
I used the following code (Similar to what you use):
private fun connectUsingNetworkSuggestion(ssid: String, password: String) {
val wifiNetworkSuggestion = WifiNetworkSuggestion.Builder()
.setSsid(ssid)
.setWpa2Passphrase(password)
.build()
// Optional (Wait for post connection broadcast to one of your suggestions)
val intentFilter =
IntentFilter(WifiManager.ACTION_WIFI_NETWORK_SUGGESTION_POST_CONNECTION);
val broadcastReceiver = object : BroadcastReceiver() {
override fun onReceive(context: Context, intent: Intent) {
if (!intent.action.equals(WifiManager.ACTION_WIFI_NETWORK_SUGGESTION_POST_CONNECTION)) {
return
}
showToast("Connection Suggestion Succeeded")
// do post connect processing here
}
}
registerReceiver(broadcastReceiver, intentFilter)
lastSuggestedNetwork?.let {
val status = wifiManager.removeNetworkSuggestions(listOf(it))
Log.i("WifiNetworkSuggestion", "Removing Network suggestions status is $status")
}
val suggestionsList = listOf(wifiNetworkSuggestion)
var status = wifiManager.addNetworkSuggestions(suggestionsList)
Log.i("WifiNetworkSuggestion", "Adding Network suggestions status is $status")
if (status == WifiManager.STATUS_NETWORK_SUGGESTIONS_ERROR_ADD_DUPLICATE) {
showToast("Suggestion Update Needed")
status = wifiManager.removeNetworkSuggestions(suggestionsList)
Log.i("WifiNetworkSuggestion", "Removing Network suggestions status is $status")
status = wifiManager.addNetworkSuggestions(suggestionsList)
}
if (status == WifiManager.STATUS_NETWORK_SUGGESTIONS_SUCCESS) {
lastSuggestedNetwork = wifiNetworkSuggestion
lastSuggestedNetworkSSID = ssid
showToast("Suggestion Added")
}
}
So here are the steps:
Install fresh version / Or remove all suggestion you added before
Make sure that you forgot all surrounding networks so your device won't auto-connect
Add wifi network suggestions list
Go to Wifi Settings to scan networks Or wait until next scan is running
A notification prompt will appear :
6. When you Press "Yes" the system will auto-connect with it via your app and internet will work normally. See the following:
Please note the following:
If you disconnect the network from Wifi Settings (i.e press disconnect bin icon in the following image) your network will be blocked for 24 hours from auto-connect even if you removed the suggested network using wifiManager.removeNetworkSuggestions(listOf(it)) and add it again. And even if you uninstall and install your app again
Unfortunately, this is limitation added by Android System as described here:
If the user uses the Wi-Fi picker to explicitly disconnect from one of the network suggestions when connected to it, then that network is blacklisted for 24 hours. During the blacklist period, that network will not be considered for auto-connection, even if the app removes and re-adds the network suggestion corresponding to the network.
If you uninstall the application while connected to suggested WiFi, the system will close the connection automatically.
In case you have multiple suggestion you can priorities them by using WifiNetworkSuggestion.Builder().setPriority(<Priority Integer>) as mentioned here:
Specify the priority of this network among other network suggestions provided by the same app (priorities have no impact on suggestions by different apps). The higher the number, the higher the priority (i.e value of 0 = lowest priority).
In case you pressed "No" in notification prompt, you can change it from (Settings > Apps & notifications > Special App access > Wi-Fi Control > App name) as described here:
A user declining the network suggestion notification removes the CHANGE_WIFI_STATE permission from the app. The user can grant this approval later by going into the Wi-Fi control menu (Settings > Apps & notifications > Special App access > Wi-Fi Control > App name).

I wish I had answers to all of your questions because I'm currently struggling with similar issues.
After many hours I was finally able to connect to the desired network using this approach:
val wifiNetworkSpecifier = WifiNetworkSpecifier.Builder()
.setSsid(ssid)
.setWpa2Passphrase(passphrase)
.setBssid(mac)
.build()
val networkRequest = NetworkRequest.Builder()
.addTransportType(NetworkCapabilities.TRANSPORT_WIFI)
.setNetworkSpecifier(wifiNetworkSpecifier)
.build()
val connectivityManager = applicationContext.getSystemService(Context.CONNECTIVITY_SERVICE) as ConnectivityManager?
connectivityManager?.requestNetwork(networkRequest, ConnectivityManager.NetworkCallback())
You can receive a whole host of events through the ConnectivityManager.NetworkCallback().

Looks like they've added support in Android 11(API 30) for adding network configuration that persists outside of the application scope and is saved as a system network configuration just like it was done with the deprecated WiFiManager method addNetwork. All you need to do is to use ACTION_WIFI_ADD_NETWORKS to show a system dialog that asks a user if he wants to proceed with adding a new Wifi suggestion to the system. This is how we start that dialog:
// used imports
import android.provider.Settings.ACTION_WIFI_ADD_NETWORKS
import android.provider.Settings.EXTRA_WIFI_NETWORK_LIST
import android.app.Activity
import android.content.Intent
import android.net.wifi.WifiNetworkSuggestion
// show system dialog for adding new network configuration
val wifiSuggestionBuilder = WifiNetworkSuggestion.Builder()
.setSsid("network SSID")
.build()
val suggestionsList = arraylistOf(wifiSuggestionBuilder)
val intent = new Intent(ACTION_WIFI_ADD_NETWORKS)
intent.putParcelableArrayListExtra(EXTRA_WIFI_NETWORK_LIST, suggestionsList);
activity.startActivityForResult(intent, 1000)
The dialog looks like this:
And then we just need to handle a result in onActivityResult method like this:
override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
if (requestCode == 1000) {
if (resultCode == Activity.RESULT_OK) {
// network succesfully added - User pressed Save
} else if (resultCode == Activity.RESULT_CANCELED) {
// failed attempt of adding network to system - User pressed Cancel
}
}
}
But as I've tested this code on Android devices that have older Android versions(lower then API30) installed I've got a crash every time I want it to show that dialog for adding a new network configuration. This is the crash:
java.lang.RuntimeException: Unable to start activity: android.content.ActivityNotFoundException: No Activity found to handle Intent { act=android.settings.WIFI_ADD_NETWORKS (has extras) }
Looks like the new way is not back-supported out of the box. So, for API30 we can use a new Intent action, for API 28 and below we can still use the old way of adding Networks, but for API29 we have some kind of gray area where I was not able to find a good solution yet. If anyone has an idea what else to do please share it with me. ;)

#Sebastian Helzer's answer works for me. I use java in my application. This may help java users...
WifiNetworkSpecifier wifiNetworkSpecifier = new WifiNetworkSpecifier.Builder()
.setSsid(ssid)
.setWpa2Passphrase(password)
.build();
NetworkRequest networkRequest = new NetworkRequest.Builder()
.addTransportType(NetworkCapabilities.TRANSPORT_WIFI)
.setNetworkSpecifier(wifiNetworkSpecifier)
.build();
ConnectivityManager connectivityManager = (ConnectivityManager)this.getApplicationContext().getSystemService(Context.CONNECTIVITY_SERVICE);
connectivityManager.requestNetwork(networkRequest, new ConnectivityManager.NetworkCallback());

How to get, inside my app, a list of printers previously settle to android printing services?

After setting up a printer through services plugin (e.g. Steps 1..3) on Android OS, my working flow should:
Press "print" button
Show dialog with available printers (previously defined on Android settings)
Execute pdf printing
Is it possible to acquire this list of available printers inside my own application? How?
So far, closest solution I got running through google's documentation was to open my pdf on a web preview and from there let Android handle everything. However, if possible, I wouldn't like to break my UX. After selecting my printer, ideal scenario would be to print pdfs directly.
Thanks in advance
------- STEPS -------
Android Printing Settings
Installed Services
Printers List

Is it possible to acquire this list of available printers inside my own application? How?
Yes you can use PrintService: https://developer.android.com/reference/android/printservice/PrintService
A print service is responsible for discovering printers, adding discovered printers, removing added printers, and updating added printers.
The Android docs also have (somewhat outdated, but still useful) lessons on using the printing-related APIs: https://developer.android.com/training/printing
This sample includes code related to printing a PDF: https://developer.android.com/training/printing/custom-docs
Sample code from the docs:
// Connect to the print manager
private fun doPrint() {
activity?.also { context ->
// Get a PrintManager instance
val printManager = context.getSystemService(Context.PRINT_SERVICE) as PrintManager
// Set job name, which will be displayed in the print queue
val jobName = "${context.getString(R.string.app_name)} Document"
// Start a print job, passing in a PrintDocumentAdapter implementation
// to handle the generation of a print document
printManager.print(jobName, MyPrintDocumentAdapter(context), null)
}
}
// Compute print document info
override fun onLayout(
oldAttributes: PrintAttributes?,
newAttributes: PrintAttributes,
cancellationSignal: CancellationSignal?,
callback: LayoutResultCallback,
extras: Bundle?
) {
// Create a new PdfDocument with the requested page attributes
pdfDocument = PrintedPdfDocument(activity, newAttributes)
// Respond to cancellation request
if (cancellationSignal?.isCanceled == true) {
callback.onLayoutCancelled()
return
}
// Compute the expected number of printed pages
val pages = computePageCount(newAttributes)
if (pages > 0) {
// Return print information to print framework
PrintDocumentInfo.Builder("print_output.pdf")
.setContentType(PrintDocumentInfo.CONTENT_TYPE_DOCUMENT)
.setPageCount(pages)
.build()
.also { info ->
// Content layout reflow is complete
callback.onLayoutFinished(info, true)
}
} else {
// Otherwise report an error to the print framework
callback.onLayoutFailed("Page count calculation failed.")
}
}

So far, no proper solution was found. Possible alternatives are:
Try to access printers through shared preferences stored by services plugins (e.g. PrintHand).
If you just to want to ease acquisition of printer's IP address & case you're using devices with bar code scanner, you could place a label on the printer with its IP Address and make a scan to store the address on a session/singleton field.
I took the second path.

How to get Bluetooth Headset battery level?

I'm trying to build an app which gets battery level of currently connected Bluetooth headset. This app can be used on phones which don't have this functionality built-in.
While searching on stackoverflow, I found How to get Bluetooth Headset battery status in android this question. I got the currently connected Bluetooth headset using BluetoothProfile.HEADSET profile.
But in the device object of type BluetoothDevice I don't see any method or property to get battery level of Bluetooth Headset.
I can get the device name and isAudioConnected.

If question is about Bluetooth HFP feature: HF indicators feature is optional for the both sides. If the both sides support it, BluetoothHeadset will broadcast BluetoothHeadset.ACTION_HF_INDICATORS_VALUE_CHANGED with BluetoothHeadset.EXTRA_HF_INDICATORS_IND_ID equal 2 (Battery Level) and BluetoothHeadset.EXTRA_HF_INDICATORS_IND_VALUE with scope 0..100. Do not remember Android version were it was implemented, you should check it.
Also battery level can be implemented in device using vendor specific HFP AT commands (especially for old handsfree devices) and maybe BLE.

I found a solution, but it only works on android 8 and above
I took this code from here
Kotlin
fun getBatteryLevel(pairedDevice: BluetoothDevice?): Int {
return pairedDevice?.let { bluetoothDevice ->
(bluetoothDevice.javaClass.getMethod("getBatteryLevel"))
.invoke(pairedDevice) as Int
} ?: -1
}

The first thing to register BroadcastReciver by "android.bluetooth.device.action.BATTERY_LEVEL_CHANGED"
and you can receive this action by the broadcast receiver then get extra data by "android.bluetooth.device.extra.BATTERY_LEVEL"
and if you want to trigger this action, you need to reconnect your Bluetooth device or Bluetooth device battery level happened to change.
Good luck for you.

Connected AirPods Pro to OnePlus 5T with Android 9.
None of those registered events happen:
"android.bluetooth.device.action.BATTERY_LEVEL_CHANGED"
"android.bluetooth.headset.profile.action.AUDIO_STATE_CHANGED"
"android.bluetooth.headset.action.HF_INDICATORS_VALUE_CHANGED"

I am Able to achieve the handset battery Level in Java
try {
BluetoothDevice device = bluetoothAdapter.getRemoteDevice("Connected device ID");
java.lang.reflect.Method method;
method = device.getClass().getMethod("getBatteryLevel");
int value = (int) method.invoke(device);
result.success(value);
} catch (Exception ex) {
result.error("invalid_argument", "'deviceId' argument is required to be string", null);
break;
}

This is #Kirill Martyuk answer as an Extension variable
val BluetoothDevice.batteryLevel
get() = this.let { device ->
val method = device.javaClass.getMethod("getBatteryLevel")
method.invoke(device) as Int?
} ?: -1
Usage would be something like
val manager = context.getSystemService(Context.BLUETOOTH_SERVICE) as BluetoothManager?
val adapter = manager?.adapter
val devices = adapter?.bondedDevices.orEmpty()
devices.forEach { device ->
Log.d("DEVICE_NAME", device.name)
Log.d("CHARGE_LEVEL", device.batteryLevel.toString())
}