What causes a power bank to catch fire? What precautions can you take?

Experts say the chances of mobile devices exploding are five in a million. PHOTO: UNSPLASH

Two passengers were slightly injured on a Scoot flight set to take off from Taoyuan International Airport in Taiwan for Singapore on Tuesday evening after a portable charger caught fire. The fire was put out and Flight TR993 was rescheduled.

The incident prompted questions on battery safety – in particular why power banks catch fire, why they are not allowed in checked-in baggage and what safety precautions users should take. Tech editor Irene Tham answers these questions and more.

Q. What causes electronic gadgets like power banks to catch fire?

A: The batteries in these gadgets are flammable.

Lithium-ion (Li-ion) batteries, first developed in the 1970s, are extremely popular because of the high amount of energy they can deliver at a given size and weight compared with nickel-metal hydride or lead acid batteries. Today, Li-ion batteries power everything from smartphones and power banks to electric vehicles and even the International Space Station.

But such batteries are inherently flammable. They store and release electrical energy through electrochemical reactions that produce heat. Lithium-based batteries can overheat under extreme conditions – such as extreme temperatures (below 0 deg C or above 65 deg C) and mechanical stress – and when designed to charge fast.

An important component in a Li-ion 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.

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 can then be generated, melting the separator, which could lead to further short-circuiting.

This is how smoke emissions, fires and explosions come about.

Battery makers tend not to use 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.

Defects in manufacturing can also produce unsafe batteries.

Q. Should consumers be worried?

A: Experts say the chances of mobile devices exploding are five in a million. But there has been an increase in the number of product recalls as well as fires due to faulty batteries in recent times.

In 2022, Singapore’s Consumer Product Safety Office (CPSO) told Harvey Norman Singapore to stop selling the Urban.Power N.Brandz PD18W 10000mAh Power Bank. The CPSO also told online retailer TMALL1688 to stop selling Portable Power Bank 20000mAh. The power banks in question caught fire during safety tests.

In October 2020, LG Electronics offered a free replacement service for the power board on 18 models of its Oled televisions that were produced from February 2016 to September 2019. This could have been due to issues with overheating.

In 2019, there were five product recalls due to faulty batteries that could overheat and pose fire hazards:

1. The OnNight 410 Trail Running Headlamp, sold between February 2014 and September 2018, recalled by retailer Decathlon.

2. Selected 15-inch MacBook Pro units sold between September 2015 and February 2017, recalled by Apple. 

3. Pocket power charger banks sold by retailer Cotton On between October 2018 and January 2019.

4. Hybrid power adaptors for power banks, recalled by Dell because of design flaws that could expose the internal components and pose an electric shock hazard.

5. HP’s battery safety recall programme was expanded to include spare batteries for its ProBook 4xx Series laptops.

In 2018, the CPSO found that 17 power banks caught fire during its safety tests, and issued alerts to retailers to stop selling them.

The world’s first major mobile phone recall took place in 2016, when Samsung recalled a total of 2.5 million of its latest flagship Samsung Galaxy Note7 devices, sparked by incidents in which they caught fire when the batteries overheated.

The number of fires that started from personal transport devices has also increased over the years. Most recently, in December 2022, a fire that engulfed a one-room flat in Woodlands started from a personal mobility aid in the unit’s living room. The device’s battery, bought online, was found to have expired.

In April 2022, a fire that broke out at a flat in Bukit Merah originated from the battery pack of an electric bicycle that was charging in the living room. In 2021, there were 32 fires involving personal mobility devices and 23 involving power-assisted bicycles.

Q. What precautions should consumers take?

A: As there is no way of telling if a battery is good or faulty, consumers should not leave devices to charge overnight. Consumers should also avoid cluttering any area where devices are plugged into power extension sockets for prolonged charging. They should also use original power cords to charge their devices.

Mechanical stress can be created when a phone or power bank is dropped. This alters the internal structure of the battery, leading to short-circuiting and overheating. Once the battery is damaged, it often swells. Consumers are advised to throw out gadgets if they see the batteries have swelled, or replace the batteries. They should also check for the presence of corrosion or a powdery residue on their batteries, which are signs of damage.

Store Li-ion batteries in a well-ventilated and dry area away from direct sunlight or heat sources. Batteries should be stacked so that they are stable and cannot be bumped, knocked over or damaged.

Buy batteries from reputable sources and use original batteries. Avoid buying second-hand batteries as there is no way to tell if they have expired. The typical estimated life of a Li-ion battery is about two to three years, or 300 to 500 charge cycles.

Q. What electronic devices must be hand-carried on a flight? What can be checked in?

A: The Federal Aviation Administration in the United States advises that devices containing lithium metal or Li-ion batteries – including laptops, smartphones and tablets – should be put in carry-on baggage when possible. When portable electronic devices powered by lithium batteries are in check-in baggage, they must be completely powered off and protected to prevent unintentional activation or damage.

Spare lithium metal and Li-ion batteries (or power banks) are prohibited in check-in baggage and must be hand-carried. It would be catastrophic if the devices combusted unnoticed in the luggage bay of the aircraft.

Similarly, the Civil Aviation Authority of Singapore requires power banks and personal transport devices powered by Li-ion batteries to be hand-carried. There is also a limit on the watt-hour (Wh) rating and lithium content for power banks and personal transport devices: 160Wh and 8g.

Join ST's Telegram channel and get the latest breaking news delivered to you.