Samsung Electronics Co. said Monday that problems with the design and manufacturing of batteries in its Galaxy Note 7 smartphones caused them to overheat and burst into fire.
The announcement of results from the company's investigation into one of its worst product fiascos comes three months after the flagship phone was discontinued.
Seven-hundred researchers and engineers tested more than 200,000 devices and more than 30,000 batteries and replicated what happened with the Note 7 phones, the world's biggest smartphone maker said in a statement.
Samsung said it was "taking responsibility for our failure to ultimately identify and verify the issues arising out of the battery design and manufacturing process."
The company recalled 2.5 million Note 7 phones in September after reports they were overheating and catching fire. It blamed lithium batteries from a supplier.
New Note 7s with different batteries also caught fire. So Samsung permanently dropped the premium phone in October. It estimates the problems will cost it at least $5.3 billion through early 2017.
Samsung has taken heat for its handling of the recall and its hasty, apparently incomplete initial investigation into what went wrong.