Apple's new iOS 18 is shaping up to be the most anticipated update yet, but it could be a nightmare for some iPhone users. 

A former employee of the tech giant has warned that the update could cause lagging and battery deterioration in older iPhones, like the X, 11, 12 and 13.

That's because iOS 18 is shaping up to be one of the biggest updates in recent years - rolling out a cutting-edge artificial-intelligence.

The new AI-powered features and other updates in the upcoming iOS 18 require more power, which could be taxing for older models. 

Apple had previously come under fire when iPhone users claimed their smartphones were being slowed down intentionally. 

The tech giant had reached a $500 million settlement with American users, which it began paying out in January, to appease a so-called 'batterygate' scandal in 2017 was labeled 'one of the largest consumer frauds in history.'

Apple agreed in 2020 to settle a class action lawsuit, but has not admitted wrongdoing.  

When the new iOS 18 launches in mid-September, it will deliver a host of new features, including 'Tap to Cash' to make paying friends easier, hidden apps, and Apple's very own artificial intelligence system: 'Apple Intelligence.'

But not everyone is excited about it. 

An ex-Apple employee took to social media to warn iPhone users about a major downside to iOS 18: it could slow down your phone.

Content creator and former Apple Sales Specialist Tyler Morgan posted a TikTok warning people with older iPhones not to download iOS 18.

'If your phone is running perfectly well and you don't care too much about the new iOS, don't update,' he said in the video.

iPhones as old as the X, which launched in 2018, can support iOS 18. But that doesn't mean it will run well on these older phones. 

'It's a new update that uses more power that's really going to drain your battery and f***ing deteriorate your battery health like crazy,' he said. 

'What happens when your battery health starts deteriorating? Your f***ing phone starts lagging,' he added. 

There are a few different reasons why your phone might be slower after installing iOS 18, according to iMyPhone, a software company that offers consulting for iPhone-related issues. 

Low data storage, having too many open apps, weak network connection, and faulty battery can all contribute to lagging after installing an iOS update, the iMyPhone website states. 

And if certain settings aren't optimized, like motion and display brightness, that can cause issues too.

Some older iPhone users who downloaded the beta version of iOS 18 have already experienced lagging. 

One Reddit user posted, 'iOS 18 has been so slow on the XR, it's crazy how bad it is. Omg. The phone has been slower than my old iPhone 6s.'

Another Reddit user made a post asking for advice about why their iPhone 13 is 'freezing and acting slow' after installing the iOS 18 beta. 

Some of these issues may stem from the fact that beta software is unfinished, and tends to be buggier than finished software, commenters responded. 

If you find your phone is lagging or dying faster after installing iOS 18 this fall, there are some solutions you can try. 

iMyPhone recommends users start with a tried-and-true fix: restarting your phone. 

This helps with retaining memory, preventing crashes, running more smoothly and prolonging battery life, the website states. 

If that doesn't work, try freeing up some storage space by deleting old photos, videos, messages and unused apps.

This should improve the speed and functionality of your phone, according to iMyPhone.

Originally announced at the company's annual Worldwide Developers Conference (WWDC) in June, iOS 18 is expected to hit devices in mid-September. 

It's packed with a bunch of new AI-powered features, like the ability to create custom emojis - or 'Genmojis' - intelligent writing tools, and big upgrades to Siri. 

It will also include the ability to 'hide' apps in locked folders, which has earned criticism from some iPhone users who say the feature could encourage cheating in relationships.  

If those features sound exciting to you, go ahead and download the update, Morgan said. But if you have an iPhone 13 or older, be prepared to experience a decline in performance.