Almost all electric bikes on the market today are made with lithium-ion batteries. Lithium-ion batteries are efficient, rechargeable batteries also used in cell phones, laptops, power tools, electric cars, and more. Although expensive, they have many great features. Relative to other batteries, they have high energy-mass, energy-volume, and power-weight ratios. Because lithium ions are relatively light and small, they are very efficient.
Lithium-ion batteries work well at high temperatures, and have relatively long lifespans, meaning that they store more energy and don’t deteriorate significantly in the long term. This is because of their high voltage and capacity. Depending on usage and care, e-bike lithium-ion batteries typically last for 3–5 years of use or 12,500 to 35,000 miles.
Lithium-ion E-bike Battery Capacity
Battery information for lithium-ion batteries in e-bikes is typically expressed in units of “Wh,” or watt hours, which are used to describe the battery’s capacity. While watts represent power, or the rate at which energy is used (energy/time), watt-hours is the energy equivalent to one watt of power used for an hour. This value represents the “size of the battery,” or battery life, and it tends to range between 200–1,000Wh for electric bike batteries. Your battery’s watt hours will be provided in your bike’s owner’s manual and will often be written on the battery itself.
The distance you’ll be able to ride with any given battery can vary significantly based on terrain, your riding style (slow and steady versus fast and aggressive), the length and frequency of your rides, and how much weight your bike is carrying. Generally, 250Wh electric batteries should last about 20–30 miles, while 750Wh electric batteries should last closer to 60–100 miles.
If your regular commute is 10 miles round trip, having an e-bike with a higher capacity battery may not be as important for you as it would be for someone who logs many more miles each day. Expect significant price differences between e-bikes of different battery sizes (sometimes up to $1,000 per 250Wh).
Battery Safety
Some people worry about electric batteries catching fire, not only for electric bikes, but also for other electric vehicles. Thermal runaway, a chain reaction caused by sudden temperature changes, causes lithium-ion batteries to explode. The process starts when the liquid electrolyte turns into a gas as a result of an increase in temperature. The electrolyte liquid in the battery can ignite when it comes in contact with oxygen.
Batteries are more likely to catch fire if stored at high temperatures or if over-charged, meaning they are left in the charger beyond the point at which the battery is full. At around 80°F, the risk of ignition/explosion increases. Being stored at this temperature also decreases the battery’s lifespan.
E-bike batteries should only be charged using the manufacturer’s cord and power adapter made specifically for that bike. Stay updated on any manufacturer’s updates about your battery and consult with the manufacturer for battery best practices. If damaged, replace your charger and battery.
Although it may not always be practical, it’s also a best practice to never leave a charging e-bike unattended. Avoid charging your battery to 100 percent to prolong your battery’s life. Charge it to 80 percent and unplug it, then let it come down to 20 percent before charging it again.
You can also check to ensure your e-bike and e-bike battery have been certified by Underwriters Laboratory, a globally recognized testing organization. In particular, it should have the “UL 2849” and “UL 2271” certifications. These indicate that the e-bike and the lithium-ion battery, respectively, have met rigorous safety standards related to fire safety.
Detachable Versus Embedded E-bike Batteries
When you purchase an e-bike, you can choose between a bike that has a detachable (removable) battery or an internal (embedded) one. Internal batteries are less likely to get stolen and are easier to charge, but detachable ones can be charged apart from the bike and are often less expensive. You might need an e-bike with a detachable battery if your storage location does not have power, for example.
Additionally, detachable batteries are easier to replace, thus maximizing the lifespan of the bike. Some people also invest in spare detachable batteries so they can quickly swap out a battery on the go, if needed.
Understanding the basics of lithium-ion batteries, including their interworkings, strengths, weaknesses, and the sizes they come in, will help you make an informed decision about which electric bike best suits you. There are some other battery types, including lead-acid, nickel-metal-hydride, and lithium iron phosphate, but lithium-ion batteries are the most common in e-bikes, by far, and the most important ones to understand.
Sources Consulted
https://www.crownbattery.com/news/extreme-weather-and-lead-acid-batteries
Which is safer, lead-acid battery or lithium battery E-bike? – Varun Electric Bike
https://www.freethink.com/energy/lithium-battery-electrolyte
https://www.ul.com/services/e-bikes-certificationevaluating-and-testing-ul-2849
Thanks also to the team at Conte’s National Landing and Trek Ballston for reviewing this article and providing feedback and additional information.
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