Samsung has revealed that irregular-sized batteries were the issue that caused Galaxy Note 7 devices to overheat, leading to an unprecedented worldwide recall of nearly three million devices.
A thinner protective layer was used around the battery device which had a higher energy density than other batteries used in Galaxy devices. This caused separate issues with the first line of Galaxy Note 7s and the replacement phones that followed the first recall.
The first batteries had a flaw in the upper right corner of the battery that caused negative electrodes to deflect, leading to higher instances of short circuiting and ultimately overheating.
The second batteries suffered from a welding defect which allowed melted copper to damage the negative electrode and cause similar short-circuiting. Some batteries were also missing insulation tape, which could have prevented overheating.
Samsung announced the results on Monday after conducting an investigation by 700 staff, who tested 200,000 devices and 30,000 batteries. The company also enlisted three independent testing firms, UL, Exponent and TUB Rheinland, to conduct their own investigations.
The smartphone maker announced a raft of safety and quality assurance measures it will implement to prevent a similar accident from happening again. This includes introducing an eight-point battery safety check, including X-ray and random battery disassembly during the manufacturing process.
Samsung also said that future designs would have more space around the battery to accommodate for a new bracket design to protect against drops.
The company is reviewing plans to share the in-depth results of its investigation into lithium-ion batteries with the wider mobile market.