Why Do E-Bike Batteries Explode? Best Practices to Prevent Battery Fires

by Nathan Schaumann

Lithium ion batteries, the kind used by the majority of e-bikes, are also found in phones, laptops, and electric cars. They work by using electrons and lithium ions moving from a negative to a positive electrode inside of a cell to create an electrical current. Because they can store such high energy in a small space, many of their components are highly flammable. 

Lithium ion batteries are made up of complex chemicals that can be triggered into combustion by a variety of factors. E-bike batteries can cause larger explosions than cell phone batteries or laptops simply because they are bigger batteries. Overheating that led to explosions in the batteries of phones and laptops has been largely eliminated through tighter regulations, safety standards and compliance testing. Now e-bikes are facing similar problems on a larger scale. 


What causes the explosions?

There are three main causes that lead to e-bike/e-scooter battery failure:

  1. Electrical 
  • This can occur because of an overcharge or over discharge, incompatibility of battery and charger, or substandard battery management system(BMS)/external short circuit. This can cause electrical currents 20 to 50 times greater than the battery is meant to handle. 
  1. Mechanical 
  • The crushing or penetration of a battery with an external object or extreme and repeated impact, such as an e-bike crash.  
  1. Thermal
  • Extreme high or low temperatures could create flammable gasses and high pressure.

“Thermal runway” is the phrase used to describe the chain reaction that takes place within a battery where one cell’s overheating leads to other cells overheating, increased pressure, the release of flammable gas, and finally an explosion. Fires can happen quickly and unpredictably, and they are hard to put out because they emit toxic fumes. Having a BMS which automatically shuts off the battery when it is operating outside of its safety zones can help eliminate this problem. 

E-bike batteries that come from safe and reputable companies are unlikely to explode if they are handled correctly and not tampered with. The main culprits of the battery explosions that have made headlines and resulted in fatalities are those that are damaged, modified, or shoddily made. Particularly worrisome is e-bike conversion kits, a kit which turns a regular bike into an e-bike. These have very few regulations and often don’t even have a battery included, leaving it up to the consumer to find a suitable battery and charger. 

Batteries from reputable manufacturers undergo certification and testing that ensures that they are safe. Overseas manufacturers that sell directly to consumers through online marketplaces are not subject to these same safety standards and are often using less expensive materials or a low quality manufacturing process in order to lower the price of their products. This greatly increases the chances of there being a defect in the battery that could lead to thermal runway.

How big is the problem?

Fires due to e-bike battery explosions “happen with some regularity — and the numbers are rising,” according to the National Fire Protection Association. In NYC, one of the main e-bike hubs, e-bike fires jumped from 30 in 2019 to 220 in 2022. In 2022, six people died due to fires caused by e-bike explosions. 

The demographic that officials in big cities like NYC are most worried about are workers who complete food deliveries using e-bikes. This group is often low-income and buys their bikes second-hand or for cheap online. They also ride the bikes up to 100 miles a day. This wear and tear on the bike increases the odds of a battery being damaged, or overcharged. Less than 10% of the batteries that this demographic uses are independently certified to be safe. 

Once the fires occur, they are also difficult to put out. Many fire extinguishers and water can cause the situation to worsen, not improve. When water reacts with lithium it produces the highly flammable gas hydrogen. 

Best Practices to Avoid Battery Fires

The biggest thing that you can do to avoid being the victim of an e-bike battery explosion is to buy your e-bike and battery from a reputable brand and only use the charger that comes with your e-bike. In the U.S., a certification from Underwriter Laboratories (UL) is an accepted safety standard.

Here are a couple additional tips to keep your e-bike safe: 

  • Unplug your bike when it is fully charged. Don’t leave it plugged in unattended, such as overnight. 
  • Do not modify or tamper with the electronics of the battery. 
  • Keep your e-bike away from external heat sources like radiators or heating vents. 
  • Don’t store your e-bike in your bedroom, by flammable materials, and if possible keep it away from places where it blocks an exit. 
  • Don’t use extension cords for charging, as they change the level of electrical resistance. 
  • If you get into a crash, be sure to assess your battery for damage. 
  • Don’t charge a battery when its overheated and don’t ride your bike if it is below -5 degrees Fahrenheit. 

If you aren’t sure about a battery’s manufacturer, get it checked out at a local bike shop or replace the battery.  If the battery overheats, there is a strange smell or noise, or the battery changes in shape or color, move it away from anything that can catch fire and call 911. 

What’s being done to solve the problem

There is pressure from lawmakers in the U.S. and other countries to demand mandatory safety standards of all battery manufacturers and confiscate any imports to their countries that don’t meet regulations. The Import Security and Fairness Act seeks to make changes to current legislation that says that items under $800 being sold directly to consumers from China don’t get inspected through customs. 

There is a proposed bill to require the Consumer Product Safety Commision to establish a safety standard for e-bikes and scooters, and the Electric Bike Incentive Kickstart for the Environment (E-BIKE) Act would institute a federal rebate toward purchase of an e-bike, but only if it meets safety standards. This could make high quality bikes more accessible to low-income consumers. Bike shops and places that sell e-bikes are also implementing better storage solutions for batteries, such as cabinets that are fire resistant from the outside and inside. 

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