Samsung has revealed why one of its flagship smartphones – the Galaxy Note 7 – was catching fire, but experts say questions remain over the company’s response.

The South Korean tech giant announced on Monday that an investigation found two separate faults with the lithium ion battery were responsible for the combustion of its phones.

Samsung Mobile chief DJ Koh told a press conference that a design flaw had caused the first batch of phones to short circuit.

DJ Koh apologised for the faults. Photo: Getty

A welding defect during manufacturing had doomed the replacement run amid a rush to release the updated version.

Mr Koh said he “deeply apologised” for the incidents, which have damaged the company’s reputation, in a live translation provided by Samsung.

He said the company was providing the results of its investigation as a “first step to regain your trust”.

The company built a standalone testing lab and gathered more than 700 researchers and engineers to test 200,000 devices and 30,000 batteries, Mr Koh said.

The phones were repeatedly charged and discharged to replicate the incident, he said.

Mr Koh added that 96 per cent of about three million phones sold worldwide had now been returned.

A replacement Samsung Galaxy Note 7 reportedly filled a US plane with smoke last year. Photo: Twitter

Samsung also announced new safety measures, including bringing some quality testing done by manufacturers in house and introducing other new quality checks.

Questions remain

Battery faults were already widely considered the culprit for the exploding phones, but Monday’s announcement has been viewed as an attempt to draw a line under the Note 7 controversy as Samsung prepares to launch a new flagship phone this year.

Samsung customers line up to get their hands on the Samsung Galaxy Note 7. Photo: Getty

However, some experts have questioned whether Samsung has done enough to deal with the issue, with the Wall Street Journal handing the company a “C grade” over its response.

“While it has developed a new 8-point battery check for future phones, we don’t have a clear sense of whether these tests will raise the bar on safety, or simply catch Samsung up to other premium smartphone makers,” wrote technology columnists Geoffrey A Fowler and Joanna Stern.

Technology analyst Foad Fadaghi, the managing director at Telsyte, said Samsung had been granted a “second chance” by consumers and that it “better hope” its response has been adequate.

“If more problems arise, it could be devastating,” he told The New Daily.

Mr Fadaghi said Samsung customers had been “surprisingly loyal to the brand”, with Telsyte data showing 60 per cent of customers still planned to purchase another of the company’s products.

“That’s second only to Apple.”

We’ve identified the cause of the Galaxy Note7 cases. Find out what happened and why it won't happen again. https://t.co/SBjhPoRhc3 pic.twitter.com/hFGlaJygJz

— Samsung Mobile (@SamsungMobile) January 23, 2017

Samsung’s Galaxy smartphones are the main competitor to the other leader in the market, Apple’s iPhone.

History of the Note 7

The faulty phones are reported to have cost the company more than $US5.3 billion ($7 billion) in operating profit.

Samsung launched the Note 7 on August 19, 2016, with the first reports of exploding phones surfacing later that month.

On September 2, sales of the phone were suspended in Australia over battery issues that caused the phone to catch fire. A recall was announced three days later.

Customers were issued with replacement phones later that month, but on October 11 sales were permanently halted over continued reports of phones catching fire.

Earlier this month, the company said 95 per cent of Note 7s has been returned by Australian customers.

Samsung’s Galaxy Note 7 smartphones have been plagued by overheating problems. Photo: AAP 

But the controversy has caused continued embarrassment for Samsung.

Air safety authorities in Australia and the US have mandated that airlines remind passengers about the dangers of the Note 7 onboard the plane.

Mr Fadaghi said the Note 7’s battery woes had handed an advantage to other Asian manufacturers and Google, which has entered the market with its Pixel smartphone.

“Samsung has left the door open to a range of competitors to make use of this scenario,” he said.

Mr Fadaghi said Samsung’s stumble had also brought increased focus on the safety of the lithium ion battery.

“Ever since the Note 7 recall, I would be surprised if most smartphone manufacturers hadn’t doubled their focus to ensure their batteries are safe,” he said.

The company is expected to unveil a new phone, the Samsung Galaxy S8, later in the year.