Perhaps one of the most useful features embedded in the new iOS 9 firmware update is the Low Power Mode setting, which, according to Apple, will extend your iPhone’s battery life for up to three additional hours.
The Low Power Mode feature can be accessed manually via the Settings application and, once activated, you have the option of putting the utility into effect automatically when the phone reaches 80% charge. Likewise, when the phone reaches 20% and 10%, respectively, the device will notify you and ask whether or not you’d like to initiate the LPM setting at that time.
According to Apple, Low Power Mode comes at a cost, however, by disabling some key features such as background data fetching, animated visual effects, and reduces the CPU performance in order to extend battery life.
Features that are either disabled or compromised when using Low Power Mode
Automatically reduces screen brightness, however the brightness can be manually increased if the luminosity doesn’t meet you needs.
Locks the screen after 30 seconds; this setting cannot be changed.
Applications will no longer automatically update content in the background.
Push updates for mail are disabled, and no notification of new mail will be displayed.
Automatic download of applications and updates is disabled.
Visual effects such as Dynamic Wallpapers and perspective zoom are disabled.
CPU performance is essentially halved. Initial reports indicate that an iPhone 6s Plus will run just as fast as an iPhone 5s when Low Power Mode is enabled.
Always on ‘Hey Siri’ feature is disabled, however Siri can still be accessed manually.
So, as you can see, it essentially all boils down to a sort of trade-off between maximizing battery life, at the expense of some performance limitations. The Low Power Mode by no means renders your device a brick, however, by disabling all of the features that make the unit a smartphone in the first place. But the cost is substantiated, all things considered, if you can actually make it through the day without having to juice up, right?