South Korean smartphone maker Samsung said on Monday that two separate flaws with the Galaxy Note 7's batteries were the causes why the premium device was pulled out of the market last year.

The first set of batteries, which was manufactured by its subsidiary Samsung SDI, reportedly had a design glitch found in the upper right corner that could cause a short circuit, the Recode reported. On the other hand, the second flaw identified, produced by Hong Kong-based Amperex Technology Ltd and used on the replacement units, had manufacturing issues that could lead to fires because of a welding defect as well as missing insulation tapes for some.

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The probe was carried out by 700 staff testing 200,000 phones and 30,000 extra batteries. Samsung also employed the services of three quality-control and supply-chain analysis firms, namely UL, Exponent, and TUV Rheinland, to help.

"It was a very painful period, but in a couple of months we learned a lot," DJ Koh, Samsung mobile head, told Recode in an interview at Samsung's office in Mountain View, California.

"I wish [that] this serves as an opportunity to improve safety of lithium-ion not only for Samsung but for the entire industry," he said, adding that the company will shoulder full responsibility for all the phone's components including the batteries made by its other subsidiaries and those from third-party firms.

Meanwhile, the Wall Street Journal reported last week citing insiders that irregularly sized batteries were the reason why some of its Galaxy Note 7 caught fire last year. Batteries manufactured by Samsung SDI did not fit properly on the phone, while those from ATL were because of the quick ramp in production to catch up the replacement demands.

"We believe if not for that manufacturing issue on the ramp (of Battery B), the Note 7 would still be in the market," Tim Baxter, Samsung's US head, said.