Technology is a story of compromises and tradeoffs. We want devices with big, pixel-dense screens. We want snappy performance and lots of RAM. But we don't want to have to keep one nervous eye on the battery-life indicator, or have to top off just to make it through the day.

iOS 9 includes a battery-saving Low Power mode, a first for Apple. This will let you flip one switch to eke out maximum power savings. iOS will shut down background activity and reduce performance to get you as much as three extra hours before the battery finally goes kaput. On Friday, MacRumors used Geekbench 3 to quantify just how big of a performance hit you can expect.

Benchmarking app Geekbench 3 ($1) was just updated to work with iOS 9, and MacRumors used it with an iPhone 6 Plus running the latest beta. In its regular state, the iPhone 6 Plus scored 1606 on the single-core processor test, and 2891 on the multicore test. With Low Power mode on, those numbers took about a 40 percent hit, to 1019 and 1751, respectively.

The story behind the story: Those Geekbench scores indicate that the iPhone 6 Plus would act more like the iPhone 5s, speedwise, but what's really cool about Low Power mode is that you can still use your phone.

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Battery life, battery strife

Up until now, a common way to save battery life is to pop open Control Center and turn off Wi-Fi and Bluetooth, shutting down those radios completely, and crank down the screen brightness as low as you can stand. To get even more, you could head to Settings > Cellular Data, and turn off LTE. Or you could go nuclear and put your iPhone in Airplane Mode, but at that point your phone is just a fancy iPod touch.

Low Power mode seems to leave all of that on. According to MacRumors, enabling Low Power decreases your iPhone's CPU speed, stops fetching new mail messages and refreshing apps in the background, and disables motion effects and animated wallpapers. That should leave your phone a lot more useful than it would have been if you'd disabled features yourself--and of course, users never had access to tweak the CPU speed themselves.

I wouldn't mind Apple expanding Low Power with a sheet of additional preferences that users could select, and a graph showing how each one might affect the bottom line. For example, some users might not mind if Low Power mode did kill Bluetooth--but anyone wearing an Apple Watch would understandably balk at that. I'd love to be able to pick and choose the features that matter to me, and still toggle the whole shebang on and off with one tap.

Or Apple could rethink its obsession with thinness and give its devices bigger batteries. (Maybe an iPhone 7 Max?) But that's far less likely. What do you think--would you buy a thicker iPhone if the battery was significantly larger? What are your favorite tips to save battery life on your devices? Let us know in the comments.

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