A faulty lithium-ion battery in an e-scooter likely caused an intense garage and house fire in Sydney’s south on Tuesday, fire investigators have found, the latest in a spate of incidents involving lithium-ion batteries.

In early November, a fire in an apartment in New Farm in inner-city Brisbane is also believed by authorities to have been sparked by an e-scooter battery. In March, batteries resulted in four separate fires in a single day in New South Wales.

Fire and Rescue NSW has referred to lithium-ion batteries as the “fastest-growing fire risk” in the state. The agency responded to 272 battery-related fires last year – more than five each week.

Fire services in both Victoria and Queensland have said they respond to lithium-ion battery fires almost every day.

Why do lithium batteries keep exploding – and what can be done to prevent fires?

What are lithium-ion batteries found in?

There are many different types of lithium-ion batteries, says Prof Amanda Ellis, head of the school of chemical and biomedical engineering at the University of Melbourne. “Overall, they’re actually very safe if they’re operated correctly.”

Lithium-ion batteries are ubiquitous – powering everything from mobile phones and computers to e-scooters, e-bikes and electric cars. They are widely used because they are able to charge quickly, deliver energy quickly and have long battery life.

The largest lithium-ion battery in Australia, known as the Victorian Big Battery, is a 300 megawatt storage battery in Geelong, which stores enough energy to power more than 1m homes for half an hour.

Why do lithium-ion batteries catch on fire?

Lithium-ion batteries, as the name suggests, contains lithium ions suspended in an electrolyte solution. The ions flow through the electrolyte, travelling back and forth between two electrodes as the battery charges and discharges.

If a lithium-ion battery is charged too fast, it can result in thermal runaway – an uncontrollable increase in temperature. “The electrolyte heats up, because there’s too much energy in the battery,” Ellis says. “It’s in a pressurised system, and so then all of a sudden – bang … it’ll crack.” The liquid electrolyte is highly flammable and will burst into flames when exposed to air.

Overheating and physical damage are the main causes of battery failure.

Lithium-ion battery fires can reach high temperatures within seconds and release highly toxic gases. Because of their chemical components, burning batteries can develop self-sustaining flames that are difficult to extinguish.

Does battery quality matter?

Battery fires can happen because of physical damage, manufacturing faults and overcharging, according to Hussein Dia, a professor of future urban mobility at the Swinburne University of Technology.

Another contributing factor, Ellis says, is that “people are thinking that all batteries are real batteries for the appliance that they have and that the cheapest one will do – that’s where the danger is”.

In EVs, batteries make up roughly 40% of the cost of the vehicle, Dia says. “There are a lot of sophisticated designs and thermal management systems that go into them – but it is not the same case in e-bikes and e-scooters.”

Statistics show that while EV fires do occur, they are rare. “They have a lower probability [of catching fire] compared to petrol or diesel cars,” Dia says. “However, for e-scooters and e-bikes the incidence is higher, and in most cases the data shows that people are either overcharging or using unapproved charging devices.”

How can you prevent a battery fire?

There are practical steps people can take to lower the chances of a lithium-ion battery fire.

Firstly, follow the manufacturer’s advice and use the approved charger.

Avoid overcharging a device’s battery. “Even with EVs, car manufacturers don’t recommend that the batteries are fully charged – a charge up to 80% should be sufficient,” Dia says.

Dia added that charging shouldn’t be unsupervised – when people are sleeping or aren’t home, for example. Fire authorities recommend that batteries be charged on hard surfaces – such as tile or concrete floors – rather than soft surfaces like beds or carpet.

“Batteries are safe but they’ve got to be operated in the conditions that they were designed for,” Ellis says.

Batteries cannot be thrown away in regular bins, because they can result in fires at waste and recycling sites, and should be recycled through dedicated battery disposal schemes.