As much as I love iPhones, and mine in particular, Which has a good case here. iPhone battery life sucks donkey tailpipe. I'd much rather have a somewhat thicker and heavier iPhone that lasts for several days.
I know you guys don't want to believe me but battery life is not that great on the iPhone. Pretty consistently I have to charge my phone if I want to leave the house at night with my 6s.
I'm not even a heavy user, most of my email is done on my laptop at work, maybe a call or two and a handful of texts, browsing social media during lunch, and the occasional web search when I'm not at my desk. I unplug my phone at 6AM and when I get home at 3:30PM I'm usually around 40-45%. Other than short drive time where I'm not streaming music or anything I am on WiFi. So if I'm just sitting on the couch watching TV/working around the house I have to plug my phone in around 7-8PM just so it doesn't die before I go to bed at 11PM. Now I have to make sure I've got portable chargers on me all the time so I don't have to worry about a dead phone while I'm on the go.
Battery life and thinness are my only complaints about the iPhone. My iPhones 4 and 5 were charged every night and sometimes didn't even last a whole day. My 6+ has always lasted me all-day but it's charged almost every night. I use book-style wallet cases just so my phone seems thicker. I know I am in the minority but I'd gladly have a thicker phone with a more powerful battery.
I am happy with my 6+'s battery for the most part but everyone I know who has a 6 or 6S is not and a couple are upgrading to the 7+ soley for battery life even though they don't want a bigger phone.