This might be something many of you are already doing, but if you get in areas of low cell signal (i.e. Your office building) and you have WiFi access you can just turn on Airplane mode, which disables everything, and then turn WiFi back on (swipe up, hit airplane, hit wifi). I've done this the last two days at the office and my battery life is significantly better...at least twice as good. It makes sense after speaking with some folks on the iOS board - T-Mobile WiFi calling no longer disables the cellular modem (it used to with Android) so that you can have seamless transfers from WiFi to LTE. However in areas of low signal where you don't need this feature it can also beat up on your battery. When you're leaving you can just swipe up and turn airplane mode off. Anyway just sharing what I learned in case it helps some others like me.