For years, people have complained about declining performance in their ageing iPhones, an issue that's commonly attributed to Apple's software updates. Something beyond a rumour percolated just last week, when a Reddit thread suggested that the cause for the slow performance could be due to Apple throttling phones with degraded batteries.

Apple now admits that it does tinker with old iPhone models. But only to make smartphones with ageing batteries run smoother and avoid shutdowns.

The disclosure came after its customers, particularly on Reddit, noticed replacing the battery on an old iPhone appeared to make it run much faster.

Batteries get worse as they age

To understand what the technology giant is up to, the first thing to know is that the battery in your device naturally degrades over time.

The more it is charged and discharged, the less battery life it has. Extreme conditions, like very hot or very cold temperatures, will also have a detrimental effect.

This is an unfortunate side effect of the lithium-ion battery, which powers a significant amount of our technology.

Apple claims its batteries should retain up to 80 per cent of their original capacity at 500 complete charge cycles — in other words, after using all of the battery's power 500 times.

What is Apple doing?

The company now admits that it may slow the smartphone's processor in the iPhone 6, iPhone 6s and iPhone SE when the battery is wearing out:

"Our goal is to deliver the best experience for customers, which includes overall performance and prolonging the life of their devices. Lithium-ion batteries become less capable of supplying peak current demands when in cold conditions, have a low battery charge or as they age over time, which can result in the device unexpectedly shutting down to protect its electronic components.

"Last year we released a feature for iPhone 6, iPhone 6s and iPhone SE to smooth out the instantaneous peaks only when needed to prevent the device from unexpectedly shutting down during these conditions.

"We've now extended that feature to iPhone 7 with iOS 11.2, and plan to add support for other products in the future."

To translate, Apple says its updates are trying to maintain the device's functionality despite a less efficient battery.

"Throttling the [central processing unit] so to avoid a reboot due to a battery that can't supply enough current is, in my opinion, a reasonable compromise," says Dr Robert Merkel, software engineering lecturer at Monash University, who has written about sluggish devices.

"I think most people would prefer their phone to slow down rather than reboot."

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