After five months of "unprecedented" testing, Samsung yesterday revealed why batteries in its failed Galaxy Note 7 smartphone were prone to overheating and fires.

Both the original battery for the device and the one used after the company's first recall had different but specific flaws that increased the chances of the positive and negative electrodes coming into contact, Samsung said. To prevent similar battery failures in the future, the company is introducing a new eight-point battery safety check.

Samsung has also created a Battery Advisory Group of chemistry, engineering and technology experts to help the company maintain "a clear and objective perspective on battery safety and innovation."

Launched in August, the Galaxy Note 7 was quickly linked to reports of overheating and fires by phone owners around the world. Samsung launched a recall, but the replacement phone experienced similar problems, causing the company to halt manufacturing of the device and begin a second recall. Of some 3 million Galaxy Note 7s sold, 96 percent have now been returned for refunds or replacements, according to Samsung.

'Unprecedented' Scale of Tests

"The scale of it is unprecedented, the scale of the investigation," Battery Advisory Group member Gerbrand Ceder said in a video released yesterday during Samsung's press conference. The tests "led to a pretty good understanding" of what caused the overheating problems in the Note 7, he said.

Samsung said it tested more than 200,000 of the Note 7 devices that were returned, as well as more than 30,000 batteries. Those tests were conducted by three separate industry organizations: UL, Exponent and TUV Rheinland.

Investigators traced problems with the battery used in the first Note 7 release to the position of the negative electrode, which caused distortions that increased the chances of overheating.

The battery in the second Note 7 that replaced the first had a different flaw: raised welding burrs on the positive electrode punched through the battery's insulation tape and separator, causing the positive and negative electrodes to touch. Some of the second-generation batteries were also found to be missing insulation tape, Samsung said.

Galaxy S8 Not Out until April

While the design problems were specific to the two types of batteries used in the Note 7, the factors leading to them affect the entire cell phone industry, according to Clare Grey, a professor of chemistry at the University of Cambridge and a member of Samsung's new Battery Advisory Group. The growing demand for small devices with high energy densities comes with the risk of putting "highly oxidized and highly reduced materials in very close proximity," she said.

While only a small number of Note 7 batteries failed, the design issues show that the industry as a whole needs to "remain vigilant," said Ceder, a professor of materials science and engineering at the University of California, Berkeley.

According to a Reuters report today, Samsung plans to delay the launch of its next flagship phone, the Galaxy S8, as it puts the new testing and safety precautions in place. Samsung normally introduces new Galaxy S phones during the Mobile World Congress in Barcelona, which runs Feb. 27-March 2, but the company is now likely to wait until April, the report said.