I have more than 100 apps installed on my iPhone 7 Plus. But I have disabled Background App Refresh for all but 2 of them. Turned off Spotlight search for non-essentials. I have notifications disabled for apps which are not important because an app is woken up from suspended state when it gets a notification. I used to have a lot of apps and games on my Android too, but greenified those non-essentials running in background. Does iOS takes care of it except of VoIP apps? I have removed Facebook and Messenger because they run as a VoIP background service. Even after disabling notifications, BAR, force-quitting, they were being updated. I did all 3 of these on Messenger. Sent myself message. Turned off Wifi/Data. Opened Messenger. The messages were there. It was confirmed when I got calls too.