You need to make sure that my Service is not killed by the system and other garbage cleaners.

The code itself:

Manifest.xml

<service
        android:name=".NotificationService"
        android:enabled="true"
        android:exported="true"
        android:permission="android.permission.RECEIVE_BOOT_COMPLETE"
        android:process=":BatMonitoring">
    </service>

    <receiver
        android:name=".BootReceiver"
        android:permission="android.permission.RECEIVE_BOOT_COMPLETED"
        android:enabled="true">

        <intent-filter>
            <action android:name="android.intent.action.BOOT_COMPLETED" />
            <action android:name="android.intent.action.QUICKBOOT_POWERON" />
            <action android:name="android.intent.action.REBOOT"/>
            <category android:name="android.intent.category.DEFAULT" />
        </intent-filter>

    </receiver>

MainActivity.java

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    intentService = new Intent(this,NotificationService.class);
    startService(intentService);
}

BootReceiver.java

public class BootReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
            Intent serviceIntent = new Intent(context, NotificationService.class);
            context.startService(serviceIntent);
    }
}

NotificationService.java

public class NotificationService extends Service {

    private NotificationManager notificationManager;
    public static final int DEFAULT_NOTIFICATION_ID = 101;

    @Override
    public void onCreate() {
        super.onCreate();
        notificationManager = (NotificationManager) this.getSystemService(NOTIFICATION_SERVICE);
        this.registerReceiver(this.mBatteryInfoReceiver, new IntentFilter(Intent.ACTION_BATTERY_CHANGED));


    }


    public int onStartCommand(Intent intent, int flags, int startId) {

        return START_STICKY;

    }
    BroadcastReceiver mBatteryInfoReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {

            int level = intent.getIntExtra(BatteryManager.EXTRA_LEVEL, -1);
            int chargeState = intent.getIntExtra(BatteryManager.EXTRA_STATUS, -1);

            int status = intent.getIntExtra(BatteryManager.EXTRA_STATUS, -1);
            boolean isCharging = status == BatteryManager.BATTERY_STATUS_CHARGING ||
                    status == BatteryManager.BATTERY_STATUS_FULL;

            switch (chargeState) {
                case BatteryManager.BATTERY_STATUS_CHARGING:

                    if (isCharging) {

                        NotificationCompat.Builder builder = new NotificationCompat.Builder(NotificationService.this)
                                .setContentTitle("Charging...")
                                .setContentText("Battery level is: " + Integer.toString(level))
                                .setSmallIcon(android.R.drawable.stat_notify_chat);

                        Notification notification = builder.build();
                        notification.defaults |= Notification.DEFAULT_VIBRATE;
                        notification.defaults |= Notification.DEFAULT_SOUND;

                        startForeground(DEFAULT_NOTIFICATION_ID, notification);

                    }
                    break;

                case BatteryManager.BATTERY_STATUS_FULL:

                    break;
                case BatteryManager.BATTERY_STATUS_DISCHARGING:

                    break;
            }

        }
    };


   @Override
    public void onDestroy () {
        super.onDestroy();

        notificationManager.cancel(DEFAULT_NOTIFICATION_ID);
        this.unregisterReceiver(this.mBatteryInfoReceiver);

        //Disabling service
        stopSelf();
    }


    public IBinder onBind(Intent intent) {
        return null;
    }
}

I took this question as one of the examples ,but it still doesn't work as it should.

I will be very grateful for any help!

UPD: Finally, the question was not solved, but if anyone needs it, then adding a restart of the service in void onDestroy () and in onTaskRemoved(Intent rootIntent) partially helped.