Yeah definitely not. Going to book one asap, background off, full bars and this has never happened until last night
The first thing I do when my battery life goes haywire is do a clean reset, set it up as a new iPhone, charge it up to full and use it like normal. Check SoT after 20% drain and estimate overall battery usage over the entire battery. If I've used 20% of my battery with anything less than an hour and a half of SoT, then I'd head up to an Apple store and get it checked out.
It could simply be an app keeping location services live all the time. Check those settings, see if it looks like something is keeping it pegged.
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My plan was to stay on the old version until it was fixed. (Bahahahahha - we all know it's not going to be fixed!)
But my IT department just told us we need to update to iOS 10 by January. I'm literally going to wait until the last minute of the last day.
People who think iOS 10 is the sole factor of bad battery life do not understand how these devices work, and everything that factors into battery life. I've seen people complain about their battery life, and I'll ask them how long it has been since they have reset their device (done a factory reset), and they'll look at me like I'm stupid. I'll further explain what I mean, and they'll tell me they've never done that in the 3 years they've owned the device.
*flips over table* Really? Would you use your computer for 3 years without having any cleanups or maintenance done on it? Would you drive your car for 3 years without changing the oil? Why do people think they can use technology for years on end without doing any kind of maintenance to ensure these devices operate properly?
Well that's potentially the problem right there...
My friends used to make fun of me because I used to format my hard drive on my computer and reinstall Windows pretty regularly (every 3-5 months), and I do the same thing with my phone. It get a clean reset every 3 months or so. However, there is one thing I can say; my devices always perform just like they did out of the box.
These devices are like mini computers. There are some settings that get changed under the hood that cause things to go haywire where the only way to fix it is a nice clean reset and a fresh install. Why? It just happens. Devices will go rogue where they won't connect to Wi-Fi for example (we have an Apple TV doing that across the street). The Wi-Fi is fine, we all use it on a daily basis. The device simply needs to be wiped and set back up. This device probably hasn't been wiped since they got the thing, and there's no telling how long that has been.
So before you blame an "update" to your OS for your poor battery life, you should at least do a factory reset and set your device up as a new device (don't restore from a backup, that's going to bring in any settings back that may be contributing), and see how it performs then.
If it's still performing poorly then there is something going on deeper than just the OS. I've been running iOS for a while on varying generations of iDevices. iPhone 5S, iPhone 6 Plus (when I had it) and now an iPhone 7 Plus, and I have had nothing short of stellar battery life on all three devices.
And your IT department is right. You shouldn't be running on an old version of iOS (or any operating system for that matter). We require all company-issued devices to immediately be updated when an OS update is released, no exceptions, unless there are known issues with that revision that break things and cause issues.