The backlash over Apple's admission it slows down older iPhones is growing.
The firm said last week it slows down phones to extend their life and stop them from shutting down as batteries age and become less effective, triggering lawsuits across the US.
In addition a South Korea's Communications Commission has reportedly asked for an explanation of the issue from Apple, while in France a consumer group has filed filed preliminary, legal complaints in court.
'We are hoping to get some answers on whether Apple intentionally restricted the performance of old iPhones and tried to hide this from customers,' the Korean Commission said.
French consumer association called 'HOP', standing for 'Stop Planned Obsolescence', has filed preliminary, legal complaints in court against Apple and Epson.
HOP said it filed its complaint against Apple in Paris on Wednesday.
A prosecutor opened an investigation into Epson last month, a judicial source said on Thursday, following a complaint filed in September by HOP in a court in the Paris suburb of Nanterre.
Laetitia Vasseur, co-founder of HOP, told Reuters the aim of both complaints was to apply the French consumer law, which was modified in 2015 to include the notion of planned obsolescence.
Apple is already facing lawsuits in the United States over accusations of having defrauded iPhone users by slowing down devices without warning to compensate for poor battery performance.
Under French law, companies risk fines of up to 5 percent of their annual sales for deliberately shortening the life of their products to spur demand to replace them.
A spokeswoman for Epson France said Epson denied the charges made against it by the HOP association.
She added that Epson was working with authorities on the matter and that the quality of its products was of the utmost importance for the company.
Officials for Apple France could not be immediately reached for comment
Some customers are unhappy the company has been less than transparent about the performance throttling feature, which they see as a ploy to drive sales of new handsets.
All the US lawsuits - filed in U.S. District Courts in California, New York and Illinois - seek class-action to represent potentially millions of iPhone owners nationwide.
A similar case was lodged in an Israeli court on Monday, the newspaper Haaretz reported.
One of the lawsuits, filed Thursday in San Francisco, said that 'the batteries' inability to handle the demand created by processor speeds' without the software patch was a defect.
'Rather than curing the battery defect by providing a free battery replacement for all affected iPhones, Apple sought to mask the battery defect,' according to the complaint.
The plaintiff in that case is represented by attorney Jeffrey Fazio, who represented plaintiffs in a $53-million settlement with Apple in 2013 over its handling of iPhone warranty claims.
The problem now seen is that users over the last year could have blamed an aging computer processor for app crashes and sluggish performance - and chose to buy a new phone - when the true cause may have been a weak battery that could have been replaced for a fraction of the cost, some of the lawsuits state.
'If it turns out that consumers would have replaced their battery instead of buying new iPhones had they known the true nature of Apple's upgrades, you might start to have a better case for some sort of misrepresentation or fraud,' said Rory Van Loo, a Boston University professor specializing in consumer technology law.
But Chris Hoofnagle, faculty director for the Berkeley Center for Law & Technology, said in an email that Apple may not have done wrong.
'We still haven't come to consumer protection norms' around aging products, Hoofnagle said.
Pointing to a device with a security flaw as an example, he said, 'the ethical approach could include degrading or even disabling functionality.'
The lawsuits seek unspecified damages in addition to, in some cases, reimbursement.
A couple of the complaints seek court orders barring Apple from throttling iPhone computer speeds or requiring notification in future instances.
Stefan Bogdanovich and Dakota Speas from Los Angeles have filed a lawsuit with the US District Court for the Central District of California.
They are accusing Apple of interfering with their devices without consent.
The pair are trying to get the case certified to cover all people in the United States who owned an Apple phone older than the iPhone 8.
Their application for the lawsuit states: 'Plaintiffs and Class Members never consented to allow Defendants to slow their iPhones.
'As a result of Defendant's wrongful actions, Plaintiffs and Class Members had their phone slowed down, and thereby it interfered with Plaintiffs' and Class Members' use or possession of their iPhones.'
A second lawsuit, filed by five plaintiffs in the Northern District of the State of Illinois, accuses Apple of deliberately keeping its power management features under wraps to persuade people to upgrade to newer devices.
'Apple's iOS updates purposefully neglected to explain that its purposeful throttling down of older model devices and resulting lost or diminished operating performance could be remedied by replacing the batteries of these devices,' the lawsuit states.
'Instead, Apple's decision to purposefully slowdown or throttle down these devices was undertaken to fraudulently induce consumers to purchase the latest iPhone versions of the iPhone 7, as well as new phones such as the iPhone 8 and iPhone X .'
In a statement sent to MailOnline, a spokesman for Apple said: '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.'
A consumer watchdog that evaluates electronic gadgets' performance sparked the outcry after it found that processing power of older models is limited once battery life begins to suffer.
Apple has come under fire for not being clear with users about the software update, or explaining when throttling happens.
The update reduces this drain on resources, allowing the phones to continue operating.
The drop in performance came to light in benchmark tests, from Toronto-based firm Geekbench.
It found that on certain versions the Apple operating system, phones with older batteries achieved much lower performance scores.
Battery capacity is expected to decrease as they age, but processor performance should stay the same.
However, users with older iPhones with lower-than-expected Geekbench scores have reported that replacing the battery increases their score, as well as the performance of the phone.
So it's true Apple intentionally slow down old iPhones. Proof: My iPhone 6 was bought 3years ago and recently got really slow. APP 'CPU DasherX' shows iPhone CPU is under clocked running at 600MHz. After a iPhone battery replacement. CPU speed resumed to factory setting 1400MHz. pic.twitter.com/pML3y0Jkp2— Sam_Si (@sam_siruomu) December 20, 2017
'I believe, as do others, that Apple introduced a change to limit performance when battery condition decreases past a certain point.
'If the performance drop is due to the 'sudden shutdown' fix, users will experience reduced performance without notification.
'Users expect either full performance, or reduced performance with a notification that their phone is in low-power mode.
'This fix creates a third, unexpected state.'
Without this warning Mr Poole believes that the fix will cause users to believe their phone is slow so they should replace it, rather than the battery which is actually at fault.
'This will likely feed into the 'planned obsolescence' narrative,' he added.
Every time Apple launches a new handset people seemingly flock to Google to ask why their current iPhone or iOS is slow.
This trend has been seen every year since Apple released the iPhone 3G in 2008.
Explanations for the slowness range from Apple's iOS causing problems on older devices to the firm deliberately slowing down old phones to make people buy the new handsets.
This latter explanation is known as planned, or built-in, obsolescence.
This is the idea that manufacturer's deliberately make their products in such a way that they become out-of-date sooner.
By doing this, the companies can encourage customers to buy the latest model of a certain product.
This also stimulates demand for products because people return again and again.
Alternatively, the so-called 'slow iPhone phenomenon' may be psychological, as people believe their phone is being sluggish even if its not.
In a blog post Felix Richter, from analytics firm Statista, said: 'Many of us know the feeling: one day we're perfectly happy with the smartphone we've been using for the past 12 months, the next day, after we've seen a colleague showing off his new gadget, ours suddenly feels inadequate, bulky and slow.
'The good news is we're not alone.'
He continued there are two possible explanations for these spikes.
The first is that it is a psychological phenomenon caused when people convince themselves their old phone is slow in comparison to the latest devices, and this could help them justify buying a new one.
The second explanation, which Mr Richter said is much more plausible, is down to the operating system not being compatible with the hardware on older phones.
New operating systems are often designed to work most effectively with the more advanced processing power and RAM seen in the newer models meaning older models can struggle to keep up.
In 2014, a study by Harvard University PhD student Laura Trucco appeared to back up conspiracy theories that Apple deliberately slows down older models of its iPhones to encourage users to buy a new release.
The study analysed worldwide searches for 'iPhone slow' and compared those results with similar searches for the term 'Samsung Galaxy slow'.
Interestingly, it discovered the term was unaffected by new releases from Samsung, but this may be due to the fact Android updates aren't rolled out at the same time like iOS ones are.
While some MailOnline readers said at the time they hadn't noticed a slow down, others claimed Apple sabotages older phones through software updates.
'This is common knowledge,' one reader wrote.
'If you want to keep your iPhone running at the same pace do not do the software upgrade that comes out within six months of a new iPhone release,'
Sendhil Mullainathan, a professor of economics at Harvard, described the results of the study as 'striking'.
But added it does not prove Apple has done anything wrong.
No matter how suggestive, he said, the data alone doesn't allow anyone to determine conclusively whether their phone is any slower.
There are other explanations for why an older model iPhone may slow down, he claims.
For instance, the latest version of the Apple operating system, iOS, is always tailored to the newest device and may therefore not work as efficiently on older models.
'Hearing about a new release makes you contemplate getting a new and faster phone,' he said. 'And you suddenly notice how slow your old phone is.'
Dom Ferkin, managing director of UK-based iOS experts, Creation Application, agrees.
He previously told MailOnline he doesn't believe Apple is doing this intentionally.
'On every hardware release they tend to upgrade the chips and they are faster every time they are released,' he said.
'Each year they release a new iOS. If you're running an iOS 7 on a 5 chip, for example, it's comparable to running Windows XP on a Windows 95 machine.
'It's just enough to annoy the users, but it's needed if you want the slew of new features that Apple releases each year.'