The smartphone manufacturer has announced the results of extensive testing into the cause of the problem, and new quality assurance measures.
Battery problems have been blamed for various instances of mobile devices including notebooks and phones overheating and even catching fire, so it hardly comes as a surprise that's the case with the Samsung Galaxy Note 7.
The Note 7 was launched on 19 August 2016, but reports of severe overheating led to the announcement of a global replacement program on 2 September. Some replacements exhibited similar issues, and the phone was discontinued on 11 October.
Today Samsung announced the results of extensive testing into the cause of the problem, as well as new quality assurance (QA) measures.
Mobile communications president DJ Koh said he deeply apologised for the problems, and thanked customers and partners for their part in achieving a 96 percent return rate of Note 7 handsets from customers.
He said Samsung tested various aspects of the Note 7 that might have affected the batteries, including the use of the fast charging option, a range of charging voltages and currents, wired and wireless charging, and a variety of preloaded and downloaded apps.
"None of these tests generated an abnormality," he said through an interpreter.
So 700 engineers conducted further charge/discharge tests on 200,000 devices and 30,000 batteries, and failures occurred at the same rate as in the field, whether or not the batteries were installed in the Note 7.
What the testing found
The results of that testing indicated the battery itself was the source of the problem, not the handset.
This conclusion was supported by investigations conducted for Samsung by testing and certification organisations UL, TUV Rheinland and Exponent.
UL found that the original batteries had a tendency to deform in one corner, and the combination of thin internal separators and stresses caused by activities such as cycling could cause an internal short circuit, leading to overheating.
The replacement batteries had somewhat different problems that could lead to the same unfortunate outcome: missing or misaligned internal insulation combined with thin separators and sharp protrusions from welds similarly led to short circuits.
Exponent came to a similar conclusion, but observed that the electrode deformation in the original battery occurred because the external pouch was too small. The replacement batteries did not have that problem, but the company agreed with UL's conclusion that internal insulation issues combined with weld defects caused the short circuits. The rest of the Note 7's battery system was not implicated, according to Exponent.
TUV Rheinland was engaged to check the manufacturing processes in China, Vietnam and Korea, along with the way batteries and assemblies were transported between the facilities. It found "no detection of relevant weakness, concern or any serious danger" but did recommend some improvements.
Koh said: "These batteries were found to be the cause of the Note 7 incidents" but added that Samsung accepted responsibility because "we provided the target" of a higher battery capacity in a more compact form.
New quality assurance measures
He said Samsung has instituted broad range of internal processes to keep product safety and quality as the top concern, including the establishment of new QA teams and the appointment of a battery advisory group drawn from academics at leading universities including Cambridge and Stanford.
Furthermore, a new eight point battery safety check includes x-ray inspection and disassembly at battery manufacturers and at Samsung's facilities, large-scale charge/discharge test, the simulation of two weeks of customer use under various scenarios, and improved training and management at all stages of battery handling.
Samsung is also making room in its devices to accommodate a new bracket design that will help protect the battery from deformation (such as when dropped), and improving device software to better control charging temperature, current and duration.
Koh said there was an opportunity to improve the safety of li-ion batteries across the whole industry, so Samsung will share information and processes with other companies, marking "a stronger commitment to quality assurance and safety."
Samsung also published an infographic explaining what went wrong...