More than 700 researchers, 200,000 devices and 30,000 batteries later, Samsung has finally revealed the cause of its defective Note 7 phones.

Faulty batteries are to blame for a spate of fires that lead to the biggest recall in mobile phone history.

Samsung said it sold 3 million Note 7 phones and had successfully recalled 96% per cent of them, leaving 120,000 Note 7 phones still out in the wild.

In a carefully worded statement that omitted any mention of the word ‘fire’, ‘burning’, or ‘exploding’, Samsung unveiled a number of new measures to avoid a repeat of such ‘incidents’.

“For the last several months, together with independent industry expert organizations, we conducted thorough investigation to find cause to the Galaxy Note7 incidents,” said DJ Koh, President of Mobile Communications Business at Samsung.

The Note 7 batteries were produced by two different companies which are referred to only as Company A and Company B in the findings.

The two companies produced batteries which each had a different set of defects.

Batteries from company A were found to have unintended damage to the negative electrode windings in the corners (see infographic 'Galaxy Note 7 -- What we discovered' below). No batteries from Company B exhibited the same fault. An additional “contributing factor” was the tip of the negative electrode being incorrectly placed in the curve and not on the planar area.

Meanwhile, batteries from Company B were found to have poor welding, resulting in high burrs which penetrated the insulation tape. In some cases, insulation tape was missing altogether.

Now you see tape...now you don't

 

In an effort to show it had exhausted all possible avenues of investigation, Samsung released copies of reports by battery specialists Exponent and UL, as well as producing a list of well-qualified academics who would advise the company on battery issues going forward.

“The scale of the investigation that Samsung did is unprecedented. I’ve never seen such a large battery of tests performed – no pun intended," said Gerbrand Ceder PhD, Professor of Material Science and Engineering, UC Berkeley. “They tested hundreds of thousands of cells to repeatedly look at what causes the failure."

Samsung has now implemented an 8-point Battery Safety Check (see infographic below) to ensure all future products are safety compliant, and formed a Battery Advisory Group of external advisers to “ensure it maintains a clear and objective perspective on battery safety and innovation”.

Bring on the 8-Point Battery Check

 

Yu Cui PhD, Professor Materials Science and Engineering Stanford University, said “consumers should have high confidence in the future products of Samsung.”

The Note 7 phone was announced in August 2016 but was recalled the following month after a series of fires around the world were blamed on the phone. It has cost Samsung around US$20 billion to recall and cancel the product.