The UK Government recently launched a consultation that seeks public and industry opinion on doubling the legal power output (not speed) from 250W to 500W on ebike models sold in the UK. The plan has sparked concerns within the fire safety community.
There is a wide range of different batteries used in ebikes, but those currently in commercial use are all based on lithium-ion technology and are supplied in various styles, shapes and sizes.
These battery packs are made of individual battery cells, which can be cylindrical like an AA battery or box-shaped like 9-volt batteries.
The batteries in ebikes consist of the assembly of many cells connected through a combination of series and parallel connections to provide the required voltage and capacity to power the bike.
Fires involving lithium-ion batteries are growing fast. While ebikes and escooters offer a great way to get around the city, if the batteries become damaged or fail, they can start incredibly ferocious fires that can quickly spread out of control.
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A recent Freedom of Information request by The Guardian found that as of May 2023, fires sparked by faulty ebikes and escooters in the UK had injured at least 190 people and killed eight.
According to the London Fire Brigade, lithium-ion battery fires represent the fastest-growing fire risk in the capital. There was a 78 per cent increase in battery fires in 2023 compared to 2022, with 155 ebike fires and 28 escooter fires recorded. In 12 months, three people died and around 60 people were injured.
Earlier, in 2021, Transport for London (TfL) banned escooters from the transport network due to the growing concern over fires.
So how are the fires started? Lithium-ion batteries contain flammable components and reactive materials. Under mechanical or thermal impact or through overcharging, these materials react with each other, generating heat accompanied by abnormal electrical behaviour and an increasing reaction rate. This results in cell rupture and the ejection of gases and sparks that can lead to fires and even explosions.
When an ebike battery catches fire, it is extremely difficult to put out because of the underlying electrochemical reactions.
Will the proposed higher-wattage batteries be even more prone to going up in smoke?
The wattage of a battery can be doubled by switching to a higher-voltage system. Increased wattage would give an ebike notably quicker acceleration, high unrestricted maximum speeds and a better ability to climb up hills. But in theory, doubling the wattage will not necessarily make the battery more likely to catch fire.
Most high-end electric bikes feature a Battery Management System (BMS), which helps prevent the overcharging or over-discharging of the battery cells. These protection circuits can help prevent the battery pack from overheating and catching fire.
However, doubling the wattage would lead to larger battery packs, increasing the risk of severe battery fires and other injuries.
Some cheaper off-brand replacements might not feature a BMS, so the battery cells can overcharge and possibly explode or drain too far, making it impossible for the battery to be recharged back to full.
While several factors can contribute to lithium-ion battery fires, the biggest risk is from the use of off-brand products.
Mechanical impact caused by dropping a battery on a hard surface or subjecting it to a severe external force is also highly likely to result in internal physical or mechanical damage, which can lead to failure and fire.
Similarly, always follow the manufacturer’s instructions when charging, storing and maintaining your battery. Contact the manufacturer directly if you are experiencing any issues or if the battery has been damaged. Most companies will replace a faulty battery if the warranty procedure has been followed.
To lessen the risk of battery fires:
- Do not open, service or tamper with batteries.
- Charge the battery pack within its recommended voltage range.
- Do not charge batteries on combustible or insulating surfaces such as beds, sofas or carpets and keep them away from highly flammable materials such as clothing and paper.
- Store batteries in a clean, dry and temperature-controlled environment. Do not store on or near heaters or in direct sunlight.
- Make sure a working smoke or heat alarm is installed in areas where devices or batteries are being charged or stored.
- Handle the battery pack carefully and avoid exposing it to sharp objects or excessive force.
- Always dispose of damaged batteries in bins intended solely for this purpose.
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