emonTX Battery Performance

I've recently installed an AA battery pack on my emonTX (previously I was running it with a USB power adaptor). I am also using 2 x 1.5V AA-LR6 hi-tech Energizer batteries (one step down from lithium batteries), which were full when I installed them a few days ago.

However, after only about 3 days of running the device, the battery voltage is down to 3.13V from about 3.24V on installation:

At this rate, the batteries will drop below 3V in a few days time, which I guess is getting close to when the microprocessor will decide it doesn't have enough power to continue working properly.

The program I am executing on the emonTX is essentially the default CT monitoring one, with a single temperature monitor and battery value added into the payload to be transmitted every 5 seconds:

void loop()
  if (CT1) {
    emontx.power = ct1.calcIrms(1480) * 240.0;                         //ct.calcIrms(number of wavelengths sample)*AC RMS voltage                                       
  float temperature = (sensors.getTempCByIndex(0));
  emontx.temperature = (temperature * 100);
  emontx.battery = ct1.readVcc();                                      //read emonTx battey (supply voltage)

  // because millis() returns to zero after 50 days !
  if (!settled && millis() > FILTERSETTLETIME) settled = true;

  if (settled)                                                            // send data only after filters have settled
    send_rf_data();                                                       // *SEND RF DATA* - see emontx_lib
    digitalWrite(LEDpin, HIGH); delay(2); digitalWrite(LEDpin, LOW);      // flash LED
    emontx_sleep(5);                                                      // sleep or delay in seconds - see emontx_lib

(Bear in mind that I have modified the payload struct etc. so the above code probably won't run on other devices by default)

Is there anything there that would be consuming the power? I have noticed various sleep commands in other examples - are these commands useful for increasing battery life? I am able to run the emonTX from a power line but I would rather not have the cables trailing into the cupboard with my mains box.

Any ideas for lowering the power consumption? The obvious one is to increase the time between transmissions of data, but does anyone have any other ideas?