@AbedKhooli Offline mode is about half the power demand of Wi-Fi mode so about 120mA would be a conservative estimate.
As far as we know currently, there should be no significant difference between running the Eggs from a USB battery power source compared to using the AC/DC power supply that comes with the Egg. To be clear, we haven't extensively studied whether the mode (offline vs wi-fi) and/or the power source (USB battery vs wall transformer) influences the measurements significantly (if at all). When we perform calibration over temperature, the units are powered by wall-transformers and connected to Wi-Fi.
We do know, however, that the gas sensors require some warm up time before their readings are stable. So even when you are operating in offline mode and battery powered, you should turn your Egg on and let it run for, I recommend, an hour before your intended data collection activity. This is obviously less of a concern in continuous monitoring situations.