Update: The 17-year-old high school student who exposed Apple's iPhone slowdown which could cost the tech-giant BILLIONS in lawsuits (Details, pics)

A 17-year-old from Tennessee exposed Apple's technique of intentionally slowing down older iPhones to force users to upgrade - something that could end up costing the company billions of dollars in class action lawsuits.

Tyler Barney, a high school student in Mt Juliet, said he discovered decreased performance has to do with phones lithium-ion batteries when his iPhone 6s 'became buggy,' according to the Tennessean. 'It was a big mess all the time. Even typing was painful. Seconds passed between keystrokes,' he said in a press release sent to outlets Friday.

Barney said that while he waited on the new updated operating system to be released by Apple, he tried his brother's older model iPhone 6.Though the phone was an older model, it was about a year younger, and he said it was noticeably faster.

He decided to look into why that might be, and found a suggestion that he replace his battery. When he did, his phone sped up instantly. Barney then took to the message board website Reddit, where he posts under the username TeckFire, to share his findings that Apple intentionally slows iPhones to extend their lives and stop them from shutting down as batteries age and become less effective.

His post went viral and led to Apple's admission 'throttling' phones to extend their life and stop them shutting down as batteries age and become less effective. On Thursday Apple issued an unprecedented apology and published a letter saying 'We know that some of you feel Apple has let you down', and revealed it is slashing the price of a replacement battery, and planning to show users exactly how much their battery has degraded.

The discovery has triggered class-action lawsuits from angry customers around the world - and will likely cause the company billions of dollars in legal fees.

'First and foremost, we have never — and would never — do anything to intentionally shorten the life of any Apple product, or degrade the user experience to drive customer upgrades,' Apple said.

'We apologize. There’s been a lot of misunderstanding about this issue, so we would like to clarify and let you know about some changes we’re making. 'Apple said it is reducing the price of an out-of-warranty iPhone battery replacement by $50 — from $79 to $29 — for anyone with an iPhone 6 or later whose battery needs to be replaced, starting in late January and available worldwide through December 2018.

'Our goal has always been to create products that our customers love, and making iPhones last as long as possible is an important part of that.'

The firm will also cut prices around the world, but has not yet revealed the pricing outside the US.