iOS 9 power-saving tactics include cutting display power for face-down devices
Better battery life is an Apple priority for iOS 9, and to that end the company has adopted extreme attention to detail, implementing things like face-down power restrictions, a Low Power mode, and a dedicated menu in the Settings app with more granular detail.

iOS 9 devices use light and proximity sensors to determine whether it's laying face-down, and stop the screen from turning on even when notifications come in. Displays are typically the most power-hungry component of any mobile device.
The Low Power mode can reduce consumption even further, mainly by limiting network activity. Email, for instance, is no longer fetched automatically, and background downloads and app refreshes are halted completely. Other measures include scaling back animations and screen brightness.
Apple is in fact promising that simply installing iOS 9 should give an iPhone 6 an extra hour of battery life. Turning on Low Power should add another three hours.
Partly because of that feature, the new Settings app moves battery options out from under a Usage submenu into a top-level section. The app can also track sources of battery usage on a narrower timeframe, recording since last wake, instead of just the past 24 hours or seven days.

iOS 9 devices use light and proximity sensors to determine whether it's laying face-down, and stop the screen from turning on even when notifications come in. Displays are typically the most power-hungry component of any mobile device.
The Low Power mode can reduce consumption even further, mainly by limiting network activity. Email, for instance, is no longer fetched automatically, and background downloads and app refreshes are halted completely. Other measures include scaling back animations and screen brightness.
Apple is in fact promising that simply installing iOS 9 should give an iPhone 6 an extra hour of battery life. Turning on Low Power should add another three hours.
Partly because of that feature, the new Settings app moves battery options out from under a Usage submenu into a top-level section. The app can also track sources of battery usage on a narrower timeframe, recording since last wake, instead of just the past 24 hours or seven days.
Comments
It would be nice if GPS/location based apps could all be restricted to "When Using". Too many apps are still all or nothing. There is no reason a traffic app (for example) needs to spin in the background using up battery when I'm at home or work.
No mention of GPS location sharing? I've long wanted my iPhone to me able to share my location with my iPad and MacBook. A simple Bluetooth protocol should be all it takes.
It is very much possible to use GPS over bluetooth. It used to be (still might be) possible using a jailbroken iphone or regular android device.
Too bad Tasker doesn't have an iOS version. This is a 6-line script.
This is good news for iPhone 4S users like me, who are still on the original battery and have to be in Airplane Mode most of the day just to make it through the day without charging.
I'm very glad Apple is still thinking of those of us who are on older hardware.
the sad thing for you is how easy it is to replace the batter on a 4S. two screws off the bottom, slide the rear off, undo one thing inside, and remove the battery. replace and close up.
On its website, Apple highlights that an iPhone -- and presumably other iOS devices -- will use light and proximity sensors to determine whether it's laying face-down, and stop the screen from turning on even when notifications come in. Displays are typically the most power-hungry component of any mobile device.
This has me really interested, because one of the constant drains on my iPhone is every time I get an email or notification, the screen always comes on.
I wonder if this will work even when your phone is in your pants pocket?
Yeah, they have a long way to go. Battery life is laughably bad in Beta 1, twice the drain rate of 6 and 7 combined if my notes are accurate. I can only assume that this is due to the new "smarter" Siri digging through my phone when it is inactive. On the upside, App compatibility is fantastic so far compared to the two previous Beta 1 versions. iOS 6 Beta 1 was notoriously bad, killing compatibility with over half the apps I had loaded on my phone at that time. I'll be ready to test my apps in another day, which is less than half the time it took to get things working right in 7. Looking forward to Beta 2.
Or am I wrong? (of course I know that Apple will do it better!)
OK, I'll say it, knowing that it won't go over well in this group: this is a feature that Samsung phones have had for a long time and advertised quite a bit: a power saving mode for when one's battery is getting low.
Or am I wrong? (of course I know that Apple will do it better!)
Nope, you're right. It's been there since the S4 at least.
I wiped my i6 and did a clean install to see if that improves battery life. Sometimes updating from previous version causes weird memory leaks and hangs that keep background processes chugging away. Resetting network settings usually fixes this, but I wanted to go tabula rasa to be sure. Going to let it sit for 7 hours with screen off and nothing running to see how it does.
The facedown thing, is used in Android already - the sensors to do it are in the iPhone since the first iPhone ever came out.
I also already use extensively the "do not disturb" feature as I work in an open space office and do not want to have my phone disturb others all the time. Not to mention that I do not need constant notification of *every single message* I receive e.g. on whatsapp etc. I can still receive phone calls from important people as per favorites settings. I am going to check my phone regularly in any case and all notifications will be there waiting for me in the lock screen.
So I wonder what battery improvement, on top of the ones I got already using this strategy, will really bring? (I now easily manage 1.5 days of usage (stand-by active use) rather than the usual 12-16; using default settings for background app refresh and geo-location)
I also agree that Apple should enforce more strict geo-location policies, as most apps have still only the "on/off" option, instead of the more intelligent "when using".
An off-topic feature I would like to see in iOS 9, not mentioned anywhere, is the iOS keeping the keyboard language chosen, *per chat*, rather than system wide. I use 3 languages regularly with people of different nationalities, and each time I switch chat, I need to switch typing language again. Why cannot it just keep the language I have been using so far in that chat/screen?
An off-topic feature I would like to see in iOS 9, not mentioned anywhere, is the iOS keeping the keyboard language chosen, *per chat*, rather than system wide. I use 3 languages regularly with people of different nationalities, and each time I switch chat, I need to switch typing language again. Why cannot it just keep the language I have been using so far in that chat/screen?
That's a really good idea.
the sad thing for you is how easy it is to replace the batter on a 4S. two screws off the bottom, slide the rear off, undo one thing inside, and remove the battery. replace and close up.
Thank you for the information, but this is not news to me.
I had looked into replacing the battery, but ultimately decided against it after reading many negative reviews of aftermarket batteries being unreliable (i.e., worse performance than used original) and sometimes even damaging iPhones. I'm currently waiting to upgrade to the 6S.
That's why you buy them from a reputable source on Amazon or eBay. I've been repairing iPhones for 4 years and have never had a single battery issue. On average, battery life doubles after replacement.