I think a lot depends on the type of flying you do. I will use three batteries and still have over 50% left but I'm just flying no pictures or videos. Everyone's usage is different it's about how much work you get it to do.Not worried about battery pack and yes i use usb large to tablet ,its a shame they cant sort out this controller charging Androids...
I found my controller battery discharged quickly when connected to my android phone. I turned off fast charging in the phone settings and the controller seems to last twice as long now