Samsung reportedly narrowed down its Galaxy Note 7 investigation to two possible reasons which could have caused an abnormally high number of units to explode. One reason that the company is currently pointing to has to do with irregularly sized batteries that didn't fit quite right into the frame of the Galaxy Note 7. The other alleged reason pertains to rampant quality control issues with replacement batteries stemming from the sharp increase in demand that battery supplier Amperex experienced when the initial recall hit units powered by Samsung SDI's batteries. Samsung will make an official statement on the matter on Monday.
The South Korean tech giant alleged that only units containing a battery made by Samsung SDI were actually dangerous from the original batch. All of the other units powered by batteries made by Amperex wound up in markets like China and were reportedly safe. A large number of Samsung SDI's batteries reportedly failed due to a slip-up in quality control that let through batteries that did not fit in the frame of the Galaxy Note 7. The pressure on these batteries caused them to fail at random as the pressure on the separator between the anode and cathode chambers would eventually break them, which resulted in the two layers meeting and causing a thermal runaway. The battery powering the Galaxy Note 7 did not have any sort of a safeguard or dampener for a thermal runaway, so such events almost always resulted in an explosion.
Batteries from Amperex, Samsung asserts, were not dangerous at the beginning of the Galaxy Note 7's lifetime. The company reportedly concluded that the only exploding unit in China powered by an Amperex-made battery did not explode because of the battery. However, after the units containing Samsung SDI's batteries were recalled and production was stopped, the responsibility to fulfill the remainder of all Galaxy Note 7 units fell on Amperex. Under tighter schedules and more demand, quality control did not catch faulty manufacturing processes that caused failing batteries, resulting in explosions caused by similar reasons to those that led to problems with Samsung SDI's batteries. This is what reportedly led to the second recall and the discontinuation of the Galaxy Note 7.