Why is Your Old iPhone being So Slow or Suddenly Shutting Down?

Apple is allegedly underclocking the CPU of iPhones with degraded batteries to prevent unintended shutdowns and extend battery life, according to numerous reports on Reddit.

Yesterday, Reddit user TeckFire posted Geekbench results before and after replacing the battery on an older iPhone 6s. Prior to replacing the battery, the device achieved a single-core benchmark score of 1466 and a multi-core score of 2512. That's well below the average of 2330 and 3984. After the battery replacement, Geekbench reported a single-core score of 2526 and a multi-core score of 4456. TechFire's battery had a wear level of around 20%.

You may remember that a year ago Apple instituted a battery replacement program after iPhone 6s users reported unexpected shutdowns. At that time they claimed only a small number of users were affected due to a manufacturing issue. The company then released iOS 10.2.1 three months later which was mysteriously able to fix unexpected shutdowns for 80% of affected iPhone 6s devices and 70% of iPhone 6 devices. It now appears as though the company started underclocking the CPU in iOS 10.2.1 if a battery in poor condition was detected.

"The increased power draw of the A8 and A9 chips will make your phone shut down when you don’t have enough voltage," says TeckFire. "This gets around it, by lowering the clock speed, so you don’t have to replace your battery, and can continue using your phone. I just wish Apple would tell us about this."

Other users have confirmed the same results. For example, Reddit user TizzleStickz posts:
Before battery replacement:
1039 single and 1749 multi
After battery replacement:
2488 single and 4435 multi

Notably, even users with the iPhone 7 are reporting the same behavior; although, newer devices have efficiency cores which would make this less noticeable.

"I observed the same behavior on an iPhone 7 (80% of design capacity). Fixed after replacing the battery," says goldcakes.

To determine if your device is being slowed down due to a degraded battery, download CPU DasherX (free) from the App Store and compare the CPU Frequency it displays with what's expected for your device.

Let us know if you've had a similar experience after replacing the battery on your device. Did performance improve?



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