My 6s had recently started to eat through its battery by 2 or 3 in the afternoon, and sometimes by noon. All would be fine, but then with all apps closed, the phone would periodically heat up and the battery level would drop like a rock. Looking at the battery usage on the phone, it turns out Safari was using 82% of my battery during the day. However I never use Safari, I use Chrome. After some digging around, I found that the culprit is Safari syncing under iCloud. I turned that off, and my battery is now 30% to 40% when I go to bed. Of course, this means that your Safari won't sync across devices, but I never found that to be super useful anyway. And, by the way, I now use Chrome across all my devices (Mac, PC, iPad, iPhone) and it works just fine compared to Safari. But why did this just start now? I have had the phone for months, and this has not been an issue. Perhaps it coincided with my switch to Chrome, but I'm not sure. Is it possible that if you do not open Safari regularly, the sync happens exclusively in the background and that process is more of a battery hog?