MainActivity.java

Intent monitorIntent = new Intent(this, BatteryLevelReceiver.class);                                                                          
PendingIntent pendingIntent = PendingIntent.getBroadcast(this.getApplicationContext(), PI_REQUEST_CODE, monitorIntent, 0);                    
AlarmManager alarmManager = (AlarmManager) getSystemService(ALARM_SERVICE);                                                                   
alarmManager.setRepeating(AlarmManager.RTC_WAKEUP, Calendar.getInstance().get(Calendar.MILLISECOND), pref_BatteryUpdatePeriod, pendingIntent);