It doesn't drain battery bad at all on my Pixel XL. Like.. No extra drain what so ever.Don't rely on Wifi calling. First it is useless if your internet goes down and second it drains your phone battery real bad. When I went to my cousin who has Xfinity but I was not able to get any signal I used Wifi calling but it really drained the phone battery. Over 10-15% overnight not even touching it. Looking at the cell signal when using Wifi calling it showed a fake cell signal with 3 to 4 bars but when you went into the battery meter I would see the cell signal a solid red. Only putting my Nexus 6P first on airplane mode then connect to his Wifi network and then turn on Wifi calling my battery was fine. If I turned on Wifi calling without airplane mode I was forced to reboot as it caused a massive wakelock which still drained my phone battery even when I turned off Wifi calling after.