The new “Low Power Mode” in iOS 9 is a pretty handy way to extend your battery life when you’re on the go; by throttling down your device’s CPU and suspending all background activity it lets you gain two to three extra hours in a pinch. You can turn it on manually by going into Settings, Battery or your iPhone, iPad, or iPod touch will offer you the option to turn it on as part of the warnings you get when your battery drains to 20 percent, and again when it hits 10 percent (assuming it’s not already on). When Low Power Mode is engaged, the standard battery icon will turn yellow to remind you that you’re in this mode.
You can also leave your device in Low Power Mode when charging it back up, however it gets shut off automatically once you reach an 80 percent charge. You’ll get a lock screen notification when this happens, and if you like, you can re-engage Low Power Mode right from the lock screen by swiping right to left and tapping “Enable Again.” This can be useful if you’re in a hurry for your iPhone to charge up, as leaving it in Low Power Mode will let your device charge faster by consuming less power while it’s charging.