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What does it take to make a cell phone user put down the phone? Thousands of Samsung Galaxy Note 7 cell phones owners continued to ignore warnings and held onto their devices, using them until replacement.

Galaxy Note 7 Sales and Use Continues after Safety Warnings

Warnings by safety agencies and technology experts that users of Samsung Galaxy Note 7 phones must power down and stop using the phones due to recent reports of explosion and fire made little impact on both sales and usage of them. As of September 14th, 87 percent of Note 7s were still actively being used.

What Makes Lithium-ion Batteries Fire-Prone

Smaller devices like cell phones, with greater processing power, are pushing batteries to the limit. To meet demands of technology, lithium-ion batteries used in cell phones have greater power storage capacity and are more volatile than lithium-ion batteries used in electric cars and in medical devices. Overcharging a lithium-ion battery or charging it above 120 degrees Fahrenheit or in temperatures below 32 degrees Fahrenheit causes “thermal runaway” and cell rupture, which may lead to combustion.

Lithium-ion Battery Misuse Disables Fail-Safe Circuitry

To reduce risk of combustion, lithium-ion battery packs contain fail-safe circuitry that disconnects the battery when its voltage is outside the safe range. However, overcharging, temperature extremes and prolonged use causes premature aging of the cells, disabling the safety mechanism.

Lithium-ion Battery Combustion Due to Manufacturing Defects

Lithium-ion batteries work by separating their positive and negative sides with a thin layer called an electrolyte, which is perforated to allow lithium ions to pass through from one side of the chamber to the other. When this happens current is generated.

After conducting product quality tests, Samsung reported that, due to a faulty manufacturing process with the Note 7 lithium-ion batteries, the positive and negative ends of the battery come into contact with each other, leading to short circuitry with overheating and combustion.

Lithium-ion technology Inherently Unsafe

Lithium-ion technology is used in almost every cellphone, laptop, tablet, camera and gaming device because it is cheap, efficient, relatively-safe and can pack a lot of charge in a small package. However, according to Vibha Kalra, PhD, professor of chemical and biological engineering in the College of Engineering at Drexel University in Drexel’s blog, “the components used in lithium-ion batteries are inherently unsafe, so even a ‘minor’ manufacturing defect or battery abuse can be dangerous.”

Samsung’s Note 7 Temporary Partial Safety Fix

The day after Samsung’s August 31st announced recall of the Note 7 phone, Samsung said it would force a special software update on some Note 7s, to prevent batteries from charging past 60 percent and overheating, while it continued to advise Note 7 users to stop using the phones and get them replaced. However, Samsung did not clarify whether it believed the updated software would make the phones permanently safe to use.

By September 16th, the Consumer Product Safety Commission (CPSC) had not announced a formal U.S. recall, and new Note 7 phones with safe batteries were not available for replacement. Without a formal CPSC-sanctioned recall, Note 7 phones were still be sold, although all major U.S. carriers stopped selling them.