As the popularity of electric bikes has grown, so have the potential safety concerns. Lithium-ion batteries are a good option for e-bike batteries because they can store a lot of energy in a small amount of space, but they can be fickle too. Reports of fires ignited by exploding e-bike batteries have grown across the country, prompting warnings by fire departments and new user education.
E-bikes have two notable components that are unique compared to a traditional bike — batteries and motors — and both can have a unique design from one to the next and a varying level of quality. Like phones, cars, bluetooth headphones, remote control cars, and so many other products, e-bikes often use lithium ion batteries.
Lithium batteries have high energy densities — up to 100x higher than a normal battery — and are made up of rechargeable cells with intercalated lithium compound or electrolyte between the anode and cathode. Lithium ion batteries are all made up of these three parts, with the electrolyte allowing electrons or ions to flow from electrode/anode (charging port) to the other electrode/cathode and vice versa.
When batteries explode, it’s said that the flow of ions has become abnormal or unstable. This could be due to a damaged or overheated battery, or overcharging a battery. There is also the possibility of contaminants within the battery due to improper manufacturing, according to the University of Washington, and it could lead to what’s called a thermal runway where the organic electrolyte within the battery is vaporized, pressurizing the battery casing, and potentially leading to an explosion when the case needs to release pressure. Some batteries have safety vents built into the case.
This appears to be how a North Vancouver resident’s e-bike battery caught fire in April, but fortunately the owner went to swap the battery and noticed the battery that had been charging was very hot. In a video on Global News Canada, one of the homeowners explains that when the battery was taken outside, it started smoking and quickly caught fire.
James Wilson of Obsession Bikes told Global News that lower-quality equipment usually causes concerns for their shop as opposed to items from Shimano, Bosch, or higher-quality e-bike brands.
A bike shop in Florida caught fire last month, destroying much of the interior and inventory, according to Bicycle Retailer and News (BRAIN). A battery which had been sent out of state for service returned to the Florida shop and was left unattended on a charger overnight. The battery came from a bike the owner hadn’t been familiar with. BRAIN noted that lithium-ion batteries, “especially those spec’d on low-cost e-bikes can present a fire hazard and should never be charged unattended, e-bike experts say.”
While no fires have been reported yet, according to a news release, a recall on Santa Cruz’s latest Heckler says that the latch mechanism that holds the battery in place can malfunction and drop the battery to the ground or the latch spring may cause wear on the battery housing over time and pose a fire risk. Consumers were informed to secure the battery prior to transporting their bikes and take them to a Santa Cruz dealer for the repair. The brand has received 10 reports of batteries falling and two reports of the latch spring wearing on the housing.
Considering how many e-bikes are on the market, the amount of fires is likely miniscule, notes a battery safety advisory from the ironically named Human Powered Solutions, however “the ramifications of a battery fire are so signficant that these relatively simple steps are more than justified.”
The document recommends a number of safety procedures for safe charging and storage and although it’s aimed at dealers, anyone charging e-bike batteries can benefit from the tips. Here are some of the major points from Human Powered Solutions and the University of Washington:
- Use a fire-resistant cabinet if possible for storage and keep it away from trash, chemicals, and other flammable items. Keep batteries stored in cabinet when not in use
- Install a smoke detector near the battery charging station or storage area
- Don’t store or charge battery packs that have been damaged. Consult a local fire department or battery recycling facility for disposal of a damaged battery pack.
- Keep batteries at room temperature, out of direct sunlight to prevent overheating
- Don’t store your battery or bike by a single exit point
- Only charge batteries with the correct charger supplied by the manufacturer. Don’t use generic or third party chargers.
- Buy only high quality batteries, preferably from the e-bike manufacturer
- Never charge a lithium-ion battery pack overnight or unattended.
- Monitor charging batteries at all times. Disconnect the battery when it is done charging and store it in a safe place.
- Never open a lithium-ion battery pack. They are not serviceable.
In an emergency:
- First, monitor your battery and look for signs of wear as you would ensure your chain is lubed.
- If a battery starts smoking, emitting unusual noises, or showing signs of melting, place the battery in a safe place, if possible.
- Call the fire department.
- It may not be possible to extinguish a lithium-ion battery fire so it’s best to mitigate other potential consequences.
- Keep a fire extinguisher nearby in the event the battery ignites something else