iOS 9’s Lower Power Mode Reduces CPU by 40% to Save iPhone Battery Life

One of the major enhancements Apple made with iOS 9 was to improve battery life: It added 1 more hour before charging was necessary. But that’s only the tip of the iceberg: iOS 9 also includes a new feature called Low Power Mode — currently limited to iPhones — which lets users gain an additional three hours of battery life. Of course, as explained by Apple, this comes at a cost: It will reduce the performance of your iDevice. To find out by how much, MacRumors decided to test it.

When your battery life approaches a critical level, you’ll be prompted to activate Low Power mode. When it’s on, it reduces the clock speed of the processor and cuts some background activities, such as limiting Mail fetching to manual, etc.


The guys over at MacRumors measured the performance of the same iPhone 6 Plus, with Low Power mode on and off, with Geekbench 3. When it’s activated, it reduces the performance of the device by about 40% (1019 single core, compared to 1606, 1751 multi-core vs. 2891). The same performance reduction was noticed on the iPhone 5s.

iOS 9 was introduced earlier this month at the annual WWDC and will be available this fall.

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  • Kael

    This is a good idea. I can live with a slow phone over a dead battery. Its a great option.

  • winnertakesteve

    I doubt I am making full use of my cpu 90% if the time anyway. Outside the occasional game I use my iPhone mostly the same I used my 3G for back in the day, with what, 50x less copy power?

    Interestingly I recall that anandtech, when reviewing the A7 chip, had indicated that a speedy processor in many cases is good for battery as it can coalesce processes and burn through them faster so the phone overall can stay in a low power state.

  • Joe Peplowski

    So far I haven’t seen a noticeably more efficient energy usage in low power mode, unfortunately. It is a few months away from being out of beta so hopefully there will be some improvements before then.