We've already seen how Apple is planning to better get around storage constraints in iOS 9 than it did in iOS 8, and folks toying around with the latest beta version of the operating system have now gotten a better understanding of how the OS improves battery life as well.
As Apple itself has already announced, the forthcoming update will include a new "Low Power Mode" that promises to add as much as three hours of battery life to your iPhone or iPad. Somewhat unsurprisingly, it turns out that's accomplished not just by disabling things like background app updates and animated wallpapers, but by throttling down the device's performance as well.
According to MacRumors, the results from a benchmarking tool suggest a fairly significant performance hit of 40 percent or so on both an iPhone 6 Plus and iPhone 5S, although it remains to be seen just how much that will be evident in average use. It's also, of course, just an option; by default, you'll be prompted to switch to Low Power Mode when your battery life drops down to 10 or 20 percent.
If performance isn't as big a concern, though, you can also choose to turn it on any time you're looking to conserve power -- which we expect will be a welcome option for folks regularly carrying around an extra battery pack (or two).