iMore

i have 2 identical 7p's. one won't download new ios updates nor install without A/C and wifi connections. the other downloads and installs ios updates with neither of the two. i can't find any settings for this automatic update behavior for ios. in 'settings'-'itunes &a app store'- there are settings for app, music, ibooks, and updates, and all are turned off---though i don't know if the one called 'updates' refers to ios updates.
any idea why my phones are acting differently?
thanks!