I was keeping my phone in airplane mode and turned off, and the battery was still draining in a day. Now it lasts three weeks. The newer the phone, the more it tries to connect with nearby phones or bluetooth devices, even when you try to disable this in the settings. That drains your battery. Also, other devices are trying to contact yours, and if your phone responds that drains the battery. Putting the phone in a Faraday bag makes it invisible as long as it is in the bag, it can't receive a signal. If it tries to send a signal, which it shouldn't if you switched that function off, the signal won't go anywhere and battery use will be minimal. Your mails and messages might pile up if they go to some cloud storage.. Yes, the just and unjust alike are hidden.