It is a conspiracy theory as old as the iPhone: Apple deliberately slows down old models when new ones come out, the rumour goes.

Apple now admits 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.

Your gadgets might slow down if they’re bloated with apps. Photo: Rawpixel/ABC

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.”

Time for a new battery

Battery degradation is an issue faced by all technology manufacturers, but some experts argue Apple should have been more transparent.

“From what I’ve seen so far, there is no way – other than a suspicion that their phone is working slowly – to know something is up, let alone how to fix it,” Dr Merkel says.

“It would have been trivial to pop up a notification when this occurs saying ‘to protect your iPhone and ensure stable operation, we have reduced your phone’s processing speed’.

“It does tend to fuel conspiracy theories that Apple is deliberately trying to push customers to newer phones, even if we take them at their word that that wasn’t their intent.”

You can pay the company $119 to install a new battery if your device is no longer under warranty, but outside options can be cheaper.

In April, the Australian Competition and Consumer Commission announced proceedings against Apple for making “false, misleading, or deceptive representations about consumers’ rights”.

It alleges Apple refused to fix malfunctioning devices that had been repaired by external companies, in contravention of Australian consumer law.

-ABC