There is no problem with the iPhone battery. The problem is with all the unnecessary crap people have constantly running in the background.
Settings > General > Background App Refresh > turn off all your app crap & turn on only what you really actually need.
Brand new, out the box iPhone , no apps loaded, sim in, lasts from a six am undock until 2-3pm with less than an hour of "screen on" time, phone gets very very hot, i have had this issue with every iphone i have owned so far except the 1st gen
problem is apple assume we all live and work in factory perfect signal los to the cell towers and build so close to the desgin spec that there is no tollerance left for less than perfect conditions, if i plug in a wifi router at work for instance (no internet connection on it, but just so the iphone has something to connect to) the battery life lasts until around 7pm from a 6am wake point... The 6Plus lasts a lot longer, but then so does the ipad mini, much bigger batteries and i think better/larger antenna in those helps reduce the power drain mobile data boosting is causing.
bottom line, the iPhones battery has always been crap if you work or live anywhere with less than a perfect cell signal, and its apples fault for not building in tolerance..
In my office, the people on iPhones are always email around asking for charging cables around lunch time, the android users (and that one weird dude with a windows phone) always seem ok.
i dont put my phones in cases, i dont use scree protectors , and if you need to carry an extra battery pack around with you, then the device was not tested in "real world" enviroments IMO
Thankfully my upgrade isnt due until march, so i think ill be skipping the iPhone 6 an 6 plus, ive heald both, and they are just too thin, and the battery life is shocking