Wesley's Tool-Box

Shortly after finishing the battery tests for the earlier post, iPhone 4S and later generations received the iOS 9.1 update. Then the thought crossed my mind that I should have tested the "Low Power Mode" introduced with iOS 9. It's a feature touted as enabling you to use the phone up to an hour more by cutting off some background activities, reduce the screen brightness, and slow down the processor. Would it equally benefit different generations of the iPhones? I ran the GeekBench 3 again to find out.

Here, the only major differentiating factor would be the processor speed because the iPhones were in airplane mode and the screen brightness was manually set to lowest like the previous tests. I did re-run the tests for the 'normal' mode because the iOS version was changed from 9.0.2 to 9.1. And as always, the values are normalized to the designed battery capacity.



This revealed that Apple's claims were not overblown. With the exception of iPhone 4S, the iPhones indeed lasted significantly longer under Low Power Mode: about one and a half hours with 5 and 5S, and about two and a half hours with the Plus phones, which are around 30 to 50% gain. It seems that the processor is clocked down to squeeze out as much battery time as possible. On the other hand, the processor for 4S can't seem to throttle back for this mode, resulting in practically no changes. This means that for 4S, the real-life battery savings would have to come from other tweaks.


And if we measure how much work is done with each mode, it gets more interesting. It confirms that the 4S isn't doing anything different, while iPhone 5 seems to fully trade battery time for speed. Meanwhile, the newer generations are able to do more work under the Low Power Mode. This means that if the tasks you do a lot on your phone isn't impacted too much by this mode, it might not be a bad idea to keep this mode on while you do those things if you want to maximize battery life.

Battery life is something most smartphone users take a big interest in, sometimes more than the raw performance. What good is a fast phone if you can't use it long enough without recharging? For iPhones, this is especially important because you can't swap out the battery without disassembling. So I decided to test this as the time allowed.

Now, each of my iPhones had been used for wildly different lengths of time, so the level of remaining battery capacity would be different as a result. This would obviously affect the tests, so I checked the capacity using iBackupBot, as you can see here.


Fortunately, batteries were mostly in good condition, having 90% or more capacity left. The brand new iPhone 6S Plus actually had slightly more than it should. Still, the difference is non-negligible. So the results of my battery tests would be normalized to the design capacity to make the comparisons fair. The 6S Plus results would be lowered a bit while the others would be boosted, all according to their respective ratios.

For a heavy-load scenario like playing a game, I used the battery test included with GeekBench 3. This is available for version 3.3 and higher, so iPhone 4 and 3GS, which can only run lower versions, had to be left out. With this test, airplane mode was turned on and the low power mode was turned off. To see how much effect the display backlight has, the test was run with both lowest and highest brightness settings.



With the screen brightness lowered, iPhone 6S Plus pulls ahead of all other previous generations. It's an impressive feat, beating the 6 Plus at the second place by about two and a half hours. The gap significantly narrows with full brightness, but it still manages to stick around slightly more. Considering that this is done with 5% less design capacity, it's certain that the 6S Plus is quite efficient despite all the enhanced performance.

Meanwhile, the battery capacity of the Plus series is so large that it has enough power left over even after driving a bigger backlight and much more screen pixels. Overall, the Plus series lasts noticeably longer than the predecessors. Curiously, the 5 and 5S don't show much difference in regards to the screen brightness compared to the other models. It seems the characteristics of the screen used for these devices were different.