Log battery level periodically

BatteryLevelReceiver.java

package com.example.battery;

import android.app.AlarmManager;
import android.app.PendingIntent;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.util.Log;

public class BatteryLevelReceiver extends BroadcastReceiver {
    private static final long DURATION = 1000 * 60 * 60; // every 1 hour
    private static final String TAG = "[battery]";
    private static final String BATTERY_TEST = "com.example.battery.BATTERY_TEST";
    @Override
    public void onReceive(Context context, Intent intent) {
        String action = intent.getAction();
        context = context.getApplicationContext();
        if (BATTERY_TEST.equals(action)) {
            IntentFilter filter = new IntentFilter(Intent.ACTION_BATTERY_CHANGED);
            context.registerReceiver(this, filter);
            context.registerReceiver(null, filter);
            
            PendingIntent operation = PendingIntent.getBroadcast(
                context,
                0,
                new Intent(action),
                PendingIntent.FLAG_UPDATE_CURRENT);
            AlarmManager alarmManager = (AlarmManager) context.getSystemService(Context.ALARM_SERVICE);
            alarmManager.set(
                AlarmManager.RTC_WAKEUP,
                System.currentTimeMillis() + 3000,
                operation);
        } else if (Intent.ACTION_BATTERY_CHANGED.equals(action)) {
            context.unregisterReceiver(this);
            int level = intent.getIntExtra("level", 0);
            Log.d(TAG, "level: " + level);
            // TODO: log battery level to file
        }
    }
}