Smoking batteries are the hot topic of the month following an unprecedented decision by Samsung, the world's largest handset maker, to pull the plug on its flagship Galaxy Note7 barely two months after its launch.
The move follows several reports that some phones emitted smoke or caught fire even after users had exchanged their original units for supposedly safe replacements during a global recall programme last month. Samsung initially put the blame on faulty batteries, but now, it seems there could be other complications.
Reader Farah Seth asked: "How do I prevent my phone battery from overheating? Is it dangerous to leave my phone to charge overnight?"
Tech Editor Irene Tham finds out why batteries now seem more prone to overheating:
Professor Rachid Yazami at the Energy Research Institute of Nanyang Technological University said the chances of mobile devices exploding or catching fire are five in a million, based on the about 20 billion lithium-based batteries in use today.
But the risk is increasing as device makers push boundaries to make batteries charge faster and last longer.
"Intense rivalry between firms might have encouraged engineers to push materials to their limits, thereby increasing risks," said Prof Yazami.
He is one of three researchers credited with laying the groundwork for today's lithium-ion battery, used in almost every consumer electronic device, including laptops, mobile phones and power banks.
He said lithium-based batteries can overheat under extreme conditions, including extreme temperatures (below 0 deg C or above 65 deg C) and mechanical stress, and when being designed to charge fast.
An important component in a battery - to prevent what is commonly known as a short circuit - is the separator between the positive (cathode) and negative (anode) electrodes. This separator is often made of a microporous polymer material.
As long as there is no rupture in the separator, there is no risk of a short circuit that could trigger overheating and a thermal runaway.
Here lies the problem: To make batteries charge faster and last longer, battery makers tend to reduce the thickness of the separator film.
During charging, the separator often comes under mechanical stress as the electrodes swell.
A thinner separator has a greater chance of rupturing, which then puts the electrodes in direct physical contact, creating a short circuit.
Intense heat will be generated, melting the separator, which could lead to further short circuiting. This is how smoking, fires and explosions come about.
Battery makers dislike thick separators as they create greater internal resistance, slowing down the charging. A thick separator also means less space for electrode materials, which store energy.
"The cost of fast charging is - unfortunately - safety," said Prof Yazami.
Since there is no way of telling if a battery is good or faulty, consumers should take the extra precaution of not leaving devices to charge overnight. Consumers should also remove any clutter when devices are plugged into power extension sockets for prolonged charging.
Samsung's move to halt production for an entire model because of overheating and fire hazard is unprecedented. But lithium-based batteries are notorious for overheating.
Although there have been no reported cases of the Note7 catching fire or exploding here, there was a report earlier this year of a deadly fire caused by drone batteries left to charge overnight.
The fire on June 9 last year engulfed a home in Parry Avenue and claimed two lives.
Overheating issues prompted electronics retailer Challenger to recall 12,000 units of its Valore portable power banks in April 2014. Nokia, Dell, Apple, Lenovo, Panasonic, Sharp, Toshiba, Hitachi and Fujitsu have also recalled products because of overheating batteries.
A version of this article appeared in the print edition of The Straits Times on October 15, 2016, with the headline 'How to keep my phone from overheating?'. Print Edition | Subscribe
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