I had iPhone 6s+, and a few week's before i got the 7+ i updated to IOS 10.0.1. I'm a light user, so i was getting at least 48-72 hrs between charge. Then after i updated to 10 i started getting less than a day of usage. I noticed the battery % decreasing rapidly. I too thought it had something to do with the software?
When i got the 7+ same thing was happening, and driving me crazy. I reset network setting's, went into notifications and turned most off. On FB, and mail i turned off show in notification center and show on lock screen. I didn't touch messages.
In privacy>location services i set most at never, and App store, Find iPhone, Google, Maps, Siri all to While using.
I have Bluetooth, and cellular off, but bluetooth on when driving. In iCloud i only have iCloud drive, keychain, and find my iPhone on. FB and Google app>settings>photo's i only turn on when i want to copy or post a pic.
I may have did other thing's but i don't remember. After i did these thing's i was getting 10hrs usage and and in the high 30 hrs standby. After i saw the improvement in battery life i decided to turn them all back because i feel if Apple preset them you should be able to have that good length of battery usage? As you can see from the pic in my other post all was going fine until my screen froze, and the phone reset @49%.Thats about the 4th or 5th time my screen has frozen.
I think there is still a lot of bugs in the software?