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Everything you need to know about e-bike batteries [from a battery engineer]
Would you be the person taking the stairs or the escalator?
I’ll be honest. barring the one-off day that I’m feeling particularly sprightly, I would just hop on the escalator with those 30 people on the right. And I’m willing to guess that most of you would too.
What we can gauge from this picture is that most people would rather do as little work as possible to get from point A to point B. This is especially true when it comes to commuting on a bike. The picture above is analogous to the difference between a regular bike and an e-bike.
Even if we address all the concerns when it comes to biking in a city (like safe biking infrastructure), we can’t expect to change fundamental human behavior. when given the option between less work or more work to achieve the same outcome, people will more likely choose to do less work.
Since getting my e-bike, I can comfortably bike from my home in Somerville to the Seaport district in Boston. a roughly 5-mile trip. in just about 20-minutes. All of a sudden, biking 5-miles is a piece of cake. I also don’t have to spend time sitting in traffic, waiting for public transit, or worry about showing up to a meeting looking like I swam across the Charles river to get there.
The beauty of an e-bike is that it makes cycling an inclusive mode of transportation because it doesn’t discriminate by age or physical ability.
When it comes to purchasing an e-bike though, there are a plethora of options for both the bike and battery. So how do you decide which one is best for your needs? As a battery engineer who has built hundreds of batteries and logged way too many hours soldering battery packs, here are my thoughts on the most commonly asked questions when it comes to e-bike batteries.
If you’re new to battery terminology, you might want to start here: Battery terms that every e-bike owner should know.
In this post, we’ll cover the following questions:
What is the best e-bike battery?
This is one of the hardest questions to answer. There are so many variables that go into what makes a good battery and what’s best for you, may not be the best for me. Even then, a good battery can perform poorly if it’s not cared for properly.
Battery packs are made up of individual battery “cells”. Cells are classified into cylindrical cells (like your AA and AAA) and prismatic cells (like the one in your phone). Each class of battery is manufactured in a variety of form-factors (in the battery world we use this term to mean size). The most commonly used form-factor of cells in an e-bike battery pack is the 18650.
A battery pack is only as good as it’s weakest cell.
When it comes to batteries, in my experience, there is a strong correlation between price and quality. I don’t follow this rule when it comes to most things like for example, box wine (I’m just saying, there are plenty of really good box wine options these days!). When it comes to batteries though, you really don’t want to be compromising on quality because you’ll eventually end up having to pay the price.
Here are some things to keep in mind when purchasing an e-bike:
Cell Manufacturers: Panasonic, LG, and Samsung have a good reputation in the battery industry for their high quality cells, so paying a premium for these cells is certainly worth it. If the e-bike you’re trying to buy doesn’t have or provide cell manufacturer information, they’re likely not going to be a reliable source anyway.
Cell Chemistry: Lithium-ion (li-ion) batteries are the best option for e-bikes. Although lead-acid batteries are significantly cheaper, they’re three times as heavy as their li-ion equivalents.
Li-ion has several variants of cell chemistry. The most popular ones for e-bikes are Nickel Manganese Cobalt (NMC), Lithium Cobalt Oxide (LCO), and Lithium Iron Phosphate (LFP). The metrics to look for when selecting a cell chemistry are:
- Specific Energy: has an impact on the range of your battery.
- Specific Power: how the battery handles high load scenarios like going up
- a hill.
- Safety: does the chemistry have a history of high in-field failures.
There are trade-offs when choosing one chemistry over another, but as we’ve shown in the image below, NMC and LFP are both great options that both offer the best value in terms of performance, price, and safety.
Picking the right battery chemistry has to do with figuring out what matters most to you. Do you want a battery that has a longer range (higher specific energy) but doesn’t have as much power? Or do you want a battery that has a more power (higher specific power) but may not last as long?
In my opinion, the best e-bike batteries are likely going to be made from cells manufactured by Panasonic, LG, or Samsung with either LFP or NMC cell chemistry.
What is the range of an e-bike battery?
The range of a battery pack depends on the amount of energy packed inside of it and is measured in Watt-Hours (Wh). Watt?
Watt-hours are calculated by multiplying the battery capacity, in Amp-hours, by the battery Voltage, in Volts.
Let’s assume that, on average, 1-mile requires about 25Wh of energy. So a 14Ah, 36V battery should get you about 25-miles per charge.
Keep in mind that the weight of the rider, outside temperature conditions, and the amount of pedaling will make a significant difference in range.
A word of caution: the range that e-bike manufacturers provide should be taken with a grain of salt. That number is generated from tests that are run in perfectly tailored lab conditions. Do you charge any of your electronics in an incubation chamber set at 28° C with a lab-grade charger that applies the perfect current while charging? Yeah, I don’t either. And so, We should assume that the manufacture-specified range is delivered only if the battery is charged and discharged under ideal conditions i.e. not real world conditions.
For a more realistic estimate, shave off 15% of the manufacturer specified range and assume this padded number to be your real range.
If you’re looking for a longer range, choose a battery that has higher capacity (Ah). If you’re looking for more power, choose a battery that has higher voltage (V). Learn more why voltage and capacity matter.
What is the lifespan of an e-bike battery?
There are several factors that affect the lifetime of a battery such as:
- environmental conditions: temperature during charging discharging
- charging rate: how fast or slow your battery is charged
- charging voltage: what voltage the battery is charged to
- depth of discharge (DoD): what voltage the battery is discharged to
The list above isn’t exhaustive but, in general, batteries decay as a function of time in the charged state. Period.
Day 1: You get your new e-bike and charge it up to 100% and go on a bike ride. When you come home, you charge the bike back up to 100% and you’re excited to ride it again soon.
Day 2. 364: Life get’s in the way and you still haven’t been out on your bike since that first ride.
Day 365: One year later, it’s the perfect day for a bike ride and you finally have some time on your hands. You head to your basement, unlock your bike, and excitedly turn it on. 80% charge. What? You clearly remember charging your bike to 100% last year before moving it to the basement!
The truth is, we can’t beat thermodynamics. I’ll say it again: batteries decay as a function of time in the charged state.
Now, because you left your battery at 100% for a whole year in a basement with no temperature control, you inadvertently caused your battery to lose a certain amount of irreversible capacity. Your range will be ~20% lower and you’ll likely have to replace your battery sooner than you expected. The table below shows you how much recoverable capacity exists in a battery after storing it at different temperatures and different charge states for 1-year.
This is why a lot of electronics come with batteries that are only partially charged. to help slow down this decay. That being said, it’s hard to track how long e-bikes and their batteries have been sitting in warehouses before being delivered to your door so you could get a battery that has been decaying for a year or two.
Manufacturers also tend to overrate their batteries and will make claims about certain batteries having a lifetime of at least 1,000 cycles. Show.me.the.data.
The lifetime of a lithium-ion battery is described as the number of cycles until the capacity (Ah) drops below 80% of it’s initial capacity. In general, this is roughly 250-400 cycles (depending on battery chemistry and other factors) which amounts to roughly 1.5 to 2 years if you charge discharge daily and care for your battery properly.
How to charge your e-bike battery to make it last longer
- The thing that will kill your battery faster than anything else is leaving it charged at elevated temperatures. If it’s 80 degrees outside and you have your e-bike fully charged, move it indoors where it’s cooler and try to drain the battery as soon as possible.
- Charge your battery at room temperature as often as possible.
- When sourcing an e-bike battery charger, the slower the charge rate the better. For example, if you have a 2-Amp charger, and your battery is a 14 Ah battery pack, you are charging at 14 Ah / 2-Amps = 7-hours. This is a nice, slow charge which will certainly improve the longevity of your battery pack. Avoid charging at rates that are faster than 2-hours for a full charge.
There’s a lot that goes into choosing the best battery for you e-bike, and there certainly isn’t a one-size-fits-all approach. But if I were buying an e-bike battery today, here’s what I’d do: LFP or NMC, slow charge, avoid storing or charging in hotter temperatures, and leave the battery at around 30% charge if you don’t plan on using it for a while.
Have questions? We’d love to help. You can get in touch using the contact form or find us on @somerville_ev
Also, subscribe below for alerts on our next post to learn more about batteries!
What’s driving the battery fires with e-bikes and scooters?
An electric bike parked near a Bronx supermarket that was destroyed in a fire that officials say was caused by a faulty lithium-ion scooter battery.
Spencer Platt/Getty Images
As firefighters battled a five-alarm fire at a supermarket in the Bronx earlier this month, New York City officials gathered beside what they said was the cause of the fire: the blackened shell of what was once a sit-on electric scooter.
Officials said that a faulty lithium-ion battery in the scooter had suddenly burst into flame, as captured on surveillance video. The resulting fire was so intense, they said, that it enveloped the building in a matter of minutes.
“There is extraordinary damage. This entire building behind me is completely destroyed. The roof is caved in. There is nothing left. And it is all because of this one single bike,” said Laura Kavanaugh, the city’s fire commissioner.
Last week’s blaze joined the more than 200 fires in New York City last year caused by batteries from e-bikes, electric scooters and similar devices. Lithium-ion battery explosions are now the third leading cause of fires in the city, the fire department says.
Per FDNY Fire Marshals, the cause of today’s 5-alarm fire at 2096 Grand Concourse in the Bronx was a lithium-ion battery which powered a scooter. piccom/HTifRojiJo
— FDNY (@FDNY) March 5, 2023
As the popularity of so-called micromobility devices has soared across the U.S., so too have risen the number of fires associated with the lithium-ion batteries that power them.
Some lawmakers and federal regulators have taken note. Late last year, the U.S. Consumer Product Safety Commission announced it had received reports of more than 200 incidents since the start of 2021 in which micromobility devices caught fire or overheated — incidents that led to the deaths of 19 people.
“Destructive and deadly fires from lithium-ion batteries in e-bikes have reached a crisis level. The tragic loss of life from battery fires is heartbreaking and preventable,” said Commissioner Richard Trumka in December.
Read on for more about why these fires are happening and how to keep yourself safe:
Why are batteries in e-bikes and scooters vulnerable to catching fire?
Lithium-ion batteries power many rechargeable devices that are part of our modern lives: cell phones, laptops, vapes, cordless power tools and electric vehicles of all kinds, from cars to scooters to e-bikes to hoverboards.
They’re small, lightweight and powerful — but they’re also prone to overheating and catching fire, said Michael Pecht, a professor of engineering at the University of Maryland. “Ever since lithium-ion batteries started to be prevalent in products, we’ve seen fires,” he said.
Fires from exploding e-bike batteries multiply in NYC — sometimes fatally
At issue is the high density of the batteries, which is a double-edged sword, said Pecht, who also serves as director of the Center for Advanced Life Cycle Engineering, a university research center that consults with companies on reliability and safety issues, including batteries.
“They can provide a lot of power to our cell phones and to our computers for a relatively long period of time in a very small volume,” he said. “But because we have so much energy packed in that small volume, if there is a problem, then they’re very flammable.”
Defects or contamination in the manufacturing process can eventually lead to short circuiting or other failures.
In 2006, Dell, Apple and other major laptop makers urged millions of customers to return laptop batteries after Sony discovered a flaw in their battery manufacturing process. Chevy, Hyundai and Chrysler have all been forced to issue recalls over battery fires in electric vehicles. The Federal Aviation Administration reported more than 60 incidents last year in which lithium-ion batteries — mostly battery packs, vapes or cell phones — overheated, began smoking or caught fire on airplanes.
Why do there seem to be more e-bike– and scooter-related fires now?
In short, there are more fires because there are so many more e-bikes and scooters these days.
Their small size and low cost relative to gas-powered vehicles have made micromobility devices an attractive transportation and recreation option for millions of Americans. That’s especially true for those living in urban areas where parking and traffic are challenges for drivers. Electric bikes and scooters have also been embraced by delivery drivers.
Safety Agency Opens Probe Into Tesla Fires
The burst in popularity is so recent that there isn’t yet much solid data about how many e-bikes, scooters and other devices are sold each year.
But what information we do have shows that their numbers are growing rapidly. The Light Electric Vehicle Association, an industry group, estimates that about 880,000 e-bikes were imported to the U.S. in 2021. That’s about double the number imported in 2020, and three times the total from 2019.
devices means more fires, experts say, especially since the industry is relatively new and unregulated, and there are a lot of different companies and products on the market.
What’s being done about it?
There’s not currently much regulation of e-bikes and scooters.
Regulation could go in several directions. One would be to require devices be certified under the safety standards recommended by Underwriter Laboratories, a group that has produced safety certifications for electric products for over a century.
Earlier this month, the New York City Council passed a package of local bills that would require all e-bikes and other electric mobility devices sold, rented or leased in the city to be certified under the appropriate UL safety standards.
Half A Million ‘Hoverboards’ Recalled Over Risk Of Fire, Explosions
The legislation also bans the sale of uncertified or used batteries. Retailers found to be in violation of the laws can be fined up to 1,000 per violation.
At the national level, the Consumer Product Safety Commission issued a letter in December calling on more than 2,000 manufacturers, importers and retailers to voluntarily adhere to UL safety standards for e-bikes and other micromobility devices.
Following the guidelines “significantly reduces the risk of injuries and deaths from micromobility device fires,” wrote Robert Kaye, the agency’s director of compliance and field operations. “Consumers face an unreasonable risk of fire and risk serious injury or death if their micromobility devices do not meet the level of safety provided by the relevant UL standards.”
Additionally, the agency has vowed to pursue penalties against companies who fail to inform the CPSC of safety hazards.
Recommendations to keep yourself safe
The main recommendation that comes from both the CPSC and the FDNY is to be present while you’re charging your device, and to not charge it while you’re sleeping. Unplug the device once it is fully charged.
The CPSC also recommends that you only use the charger that came included with your device and to follow the manufacturer’s instructions for proper charging.
Fire officials add that you should charge your device away from flammable materials like furniture and pillows, and that you shouldn’t charge or store your device in a location that blocks your access to an exit.
When you’re buying an e-bike or other micromobility device, try to find what battery comes stocked with it, Pecht said. Does the maker of the device state where the battery is sourced from? Is the battery made by a reputable manufacturer? Experts also suggest that consumers look for batteries that have a UL certification.
High demand and for lithium send mines into overdrive
Be warned that some online sellers may falsely claim to have UL certification. Others may sell “re-wrapped” batteries, meaning counterfeit batteries produced to appear as though they’re made by reputable manufacturers.
If your battery starts to fail, it may be safest to buy a new one. “Don’t repair anything yourself, and buy from a company where you know that they’re using brand-name batteries,” Pecht said. It may work best to buy a new battery from the same company that produced your bike or scooter.
To dispose of an old battery, bring it to a battery recycling center or other e-waste facility. Don’t throw away lithium-ion batteries in conventional trash.
What’s driving the battery fires with e-bikes and scooters?
An electric bike parked near a Bronx supermarket that was destroyed in a fire that officials say was caused by a faulty lithium-ion scooter battery.
Spencer Platt/Getty Images
As firefighters battled a five-alarm fire at a supermarket in the Bronx earlier this month, New York City officials gathered beside what they said was the cause of the fire: the blackened shell of what was once a sit-on electric scooter.
Officials said that a faulty lithium-ion battery in the scooter had suddenly burst into flame, as captured on surveillance video. The resulting fire was so intense, they said, that it enveloped the building in a matter of minutes.
“There is extraordinary damage. This entire building behind me is completely destroyed. The roof is caved in. There is nothing left. And it is all because of this one single bike,” said Laura Kavanaugh, the city’s fire commissioner.
Last week’s blaze joined the more than 200 fires in New York City last year caused by batteries from e-bikes, electric scooters and similar devices. Lithium-ion battery explosions are now the third leading cause of fires in the city, the fire department says.
Per FDNY Fire Marshals, the cause of today’s 5-alarm fire at 2096 Grand Concourse in the Bronx was a lithium-ion battery which powered a scooter. piccom/HTifRojiJo
— FDNY (@FDNY) March 5, 2023
As the popularity of so-called micromobility devices has soared across the U.S., so too have risen the number of fires associated with the lithium-ion batteries that power them.
Some lawmakers and federal regulators have taken note. Late last year, the U.S. Consumer Product Safety Commission announced it had received reports of more than 200 incidents since the start of 2021 in which micromobility devices caught fire or overheated — incidents that led to the deaths of 19 people.
“Destructive and deadly fires from lithium-ion batteries in e-bikes have reached a crisis level. The tragic loss of life from battery fires is heartbreaking and preventable,” said Commissioner Richard Trumka in December.
Read on for more about why these fires are happening and how to keep yourself safe:
Why are batteries in e-bikes and scooters vulnerable to catching fire?
Lithium-ion batteries power many rechargeable devices that are part of our modern lives: cell phones, laptops, vapes, cordless power tools and electric vehicles of all kinds, from cars to scooters to e-bikes to hoverboards.
They’re small, lightweight and powerful — but they’re also prone to overheating and catching fire, said Michael Pecht, a professor of engineering at the University of Maryland. “Ever since lithium-ion batteries started to be prevalent in products, we’ve seen fires,” he said.
Fires from exploding e-bike batteries multiply in NYC — sometimes fatally
At issue is the high density of the batteries, which is a double-edged sword, said Pecht, who also serves as director of the Center for Advanced Life Cycle Engineering, a university research center that consults with companies on reliability and safety issues, including batteries.
“They can provide a lot of power to our cell phones and to our computers for a relatively long period of time in a very small volume,” he said. “But because we have so much energy packed in that small volume, if there is a problem, then they’re very flammable.”
Defects or contamination in the manufacturing process can eventually lead to short circuiting or other failures.
In 2006, Dell, Apple and other major laptop makers urged millions of customers to return laptop batteries after Sony discovered a flaw in their battery manufacturing process. Chevy, Hyundai and Chrysler have all been forced to issue recalls over battery fires in electric vehicles. The Federal Aviation Administration reported more than 60 incidents last year in which lithium-ion batteries — mostly battery packs, vapes or cell phones — overheated, began smoking or caught fire on airplanes.
Why do there seem to be more e-bike- and scooter-related fires now?
In short, there are more fires because there are so many more e-bikes and scooters these days.
Their small size and low cost relative to gas-powered vehicles have made micromobility devices an attractive transportation and recreation option for millions of Americans. That’s especially true for those living in urban areas where parking and traffic are challenges for drivers. Electric bikes and scooters have also been embraced by delivery drivers.
Safety Agency Opens Probe Into Tesla Fires
The burst in popularity is so recent that there isn’t yet much solid data about how many e-bikes, scooters and other devices are sold each year.
But what information we do have shows that their numbers are growing rapidly. The Light Electric Vehicle Association, an industry group, estimates that about 880,000 e-bikes were imported to the U.S. in 2021. That’s about double the number imported in 2020, and three times the total from 2019.
devices means more fires, experts say, especially since the industry is relatively new and unregulated, and there are a lot of different companies and products on the market.
What’s being done about it?
There’s not currently much regulation of e-bikes and scooters.
Regulation could go in several directions. One would be to require devices be certified under the safety standards recommended by Underwriter Laboratories, a group that has produced safety certifications for electric products for over a century.
Earlier this month, the New York City Council passed a package of local bills that would require all e-bikes and other electric mobility devices sold, rented or leased in the city to be certified under the appropriate UL safety standards.
Half A Million ‘Hoverboards’ Recalled Over Risk Of Fire, Explosions
The legislation also bans the sale of uncertified or used batteries. Retailers found to be in violation of the laws can be fined up to 1,000 per violation.
At the national level, the Consumer Product Safety Commission issued a letter in December calling on more than 2,000 manufacturers, importers and retailers to voluntarily adhere to UL safety standards for e-bikes and other micromobility devices.
Following the guidelines “significantly reduces the risk of injuries and deaths from micromobility device fires,” wrote Robert Kaye, the agency’s director of compliance and field operations. “Consumers face an unreasonable risk of fire and risk serious injury or death if their micromobility devices do not meet the level of safety provided by the relevant UL standards.”
Additionally, the agency has vowed to pursue penalties against companies who fail to inform the CPSC of safety hazards.
Recommendations to keep yourself safe
The main recommendation that comes from both the CPSC and the FDNY is to be present while you’re charging your device, and to not charge it while you’re sleeping. Unplug the device once it is fully charged.
The CPSC also recommends that you only use the charger that came included with your device and to follow the manufacturer’s instructions for proper charging.
Fire officials add that you should charge your device away from flammable materials like furniture and pillows, and that you shouldn’t charge or store your device in a location that blocks your access to an exit.
When you’re buying an e-bike or other micromobility device, try to find what battery comes stocked with it, Pecht said. Does the maker of the device state where the battery is sourced from? Is the battery made by a reputable manufacturer? Experts also suggest that consumers look for batteries that have a UL certification.
High demand and for lithium send mines into overdrive
Be warned that some online sellers may falsely claim to have UL certification. Others may sell “re-wrapped” batteries, meaning counterfeit batteries produced to appear as though they’re made by reputable manufacturers.
If your battery starts to fail, it may be safest to buy a new one. “Don’t repair anything yourself, and buy from a company where you know that they’re using brand-name batteries,” Pecht said. It may work best to buy a new battery from the same company that produced your bike or scooter.
To dispose of an old battery, bring it to a battery recycling center or other e-waste facility. Don’t throw away lithium-ion batteries in conventional trash.