One of the new features we highlighted in iOS 9 is an innovative new way to help your iPhone battery make it through a long day. When toggled on, Low Power mode automatically kicks in when your battery level starts to get low, reducing the clock speed of the CPU as well as cutting some background activities.
MacRumors ran some tests in Geekbench 3 to measure the performance reduction when Low Power mode was activated, and found it to reduce the performance of an iPhone by around 40%. This would mean that your iPhone 6 would end up with performance somewhere between that of an iPhone 5 and an iPhone 5s.
Apple tweaked the description of Low Power mode in iOS 9 Beta 2.
Low Power mode temporarily reduces power consumption until you can fully charge your iPhone. When this is on, mail fetch, background app refresh, automatic downloads, and some visual effects are reduced or disabled.
The previous text indicated that motion effects and animated wallpapers are disabled. The battery icon turns yellow when Low Power mode is engaged, and it’s been suggested that battery life could be extended by up to three hours.
In addition to helping you get more from your battery, iOS 9 also helps you make the most of your storage capacity.