Electric Bike Battery Fires and How to Prevent Them [VIDEO]

A lithium ion electric bike battery pack with its cells exposed.By Edward Benjamin, Lead Instructor of the Light Electric Vehicle Association Technician Training.

For a battery of any sort to catch fire is rare. For an electric bicycle battery to catch fire is, perhaps, even more rare.

There are about 220 million electric bikes in daily service around the globe, and fires are so rare as to attract international attention. (And keep in mind that cell phone batteries and computer batteries also, but rarely, catch fire.)

As an avid collector of ebike battery fire stories, I know of less than 20 such fires over a period of 20 years and more than 200 million ebikes in use.

Even so, there are a few recent stories in the media about fires that were caused by batteries on electric bicycles. Most of them at bike shops. And this raises questions.

The cause of these fires is often described as “battery for an electric bike that was charging”.  (This reminds me of the family owned bike shop in the USA that burned down due to an electric drill on charge. That same family had a home burn due to another power tool on charge. Keep in mind that what is described here is applicable to all rechargeable batteries.) And often “charging over night”.

Electric bike batteries are ‘Large Format’ batteries, and these involve a lot more material when there is a problem. So some extra care is warranted, when compared to charging your cell phone.

All batteries have the potential for fire, or even explosion. When enough energy is crammed into a shoe box sized case to carry the rider 20 miles at 20 mph, up hill and down…keeping it under control becomes an issue.

Even your automobile starter battery carries a warning about fire and explosion if incorrectly charged. Close to the end of this article, you will find a listing of the comparable flammability of various batteries. The short summary is: They will all burn, but it is vanishingly rare for them to do so.

The author notes that in every case that he has learned about, the fire resulted while the battery charger was plugged in and connected to the battery or bike. That gives us some guidance on how to prevent such problems.

In at least one case, the battery was being charged with an incorrect charger. One that looked like the correct charger but was actually a power supply for a completely different purpose. In another case, the battery was under charge using a lead acid charger on a lithium battery. But there have been cases of the correct charger leading to a smoking battery, or a fire as well.

Lead acid batteries, used on the least expensive ebikes, are regarded as very stable. But they can be overcharged, and that can lead to a fire, so even on lead acid bikes, care must be taken, and a charger that will turn itself off when the charge is complete (smart charger) is preferred for all electric bike applications.

While lead acid batteries are generally thought to not need a Battery Management System (BMS), all lithium batteries, and the rarer NiMH battery should have such a system installed.

A BMS will protect the battery (and the consumer) from overcharge, over discharge, thermal runaway, short circuits and more. When a hazardous condition is detected by the microchip controlling a BMS, it will open solid state switches to turn off, and isolate the battery and affected cells.  For an ebike, the BMS is a small printed circuit board that is installed adjacent to the cells of the battery. (In your cell phone and computer, it is often a function of the micro chip that operates the phone or computer.) When a BMS is installed and working properly, there is almost no chance of a fire.

Additionally, many cell makers use components in the cell itself that will shut the cell down in the event of high temperature, or will vent flammable gases before they can be dangerous. Some battery packagers use material that will melt, absorbing heat as it does so, and further reduce chance of fire. AllCell is one maker of such materials.

allcell battery thermal management

AllCell battery thermal management material

But, here is a list of things that a consumer or a dealer can do to protect themselves from such a fire.

1. Buy quality. However… high price does not ensure a quality battery. Cells are made by many different companies, with a few, such as Tianjin Lishen, Samsung, Panasonic, LG, being famous and reputable.

But these companies only make the cells, which are then combined into packages of 10 to 40 or more cells to create the battery that powers the bike. The battery packager must correctly weld these cells together, and install an appropriate Battery Management System (BMS).  One recent study concluded that almost all “battery problems” were actually “battery package assembler defects”.

Big brand names like the ones listed here pay attention to the end users, the packagers, and the after sales service of batteries using their cells. So a battery package using such cells is a good start. But…it is not unusual for there to be inaccurate claims that such brand name cells are used (and they are often not marked, even in legitimate packages.) when the truth is that the cells used are the least expensive that can be found from dodgy makers.

2. Ask questions, and if you do not get good and open answers, move on.

Dealers – you and your insurance company deserve to know what cells are being used, who the battery package assembler is, the features of the BMS, who made the charger, and to have an insurance certificate from a  reputable company that names you as additionally insured.

3. ONLY USE THE CHARGER THAT CAME WITH THE BIKE! This is actually harder to do that it might seem.

In the bike shop there may be several bikes and several chargers that can be connected incorrectly. Too many chargers look the same and use the same fittings. So at the bike shop, always tag the charger in an unmistakeable way as to which bike it is used for.

And at home, when there is more than one ebike in residence, do the same.

4. Read the info on the side of the charger. It will identify the type of battery it is intended for and the voltage. Consider if this is the correct info for your bike. I like to put the name of the bike on the charger with a marking pen.

5. Keep an eye on the charger. Most have a light that will indicate that the charge is complete. Leaving the charge connected and plugged in is not needed, and potentially hazardous. And leads to wearing out the charger as well.

6. Read the owners manual. All of it, including the warnings.

7. Dealers, keep in mind that you will often handle batteries that you do not know much about. Some of them may be damaged, or the consumer may have misinformed you about what has happened to that battery (I was just riding along ….). Some of the batteries you will handle will be defective or very poor quality and you are the place that such problems will come to. At the bike shop, you need to exercise extreme caution and how to do it is described below.

8. At home, charge batteries in a dry, sheltered place, where a problem battery can be moved outside instantly. And do NOT charge them overnight. Charge while you are awake and alert to smells, smoke, etc.

9. Never attempt to charge a damaged battery. Or one that might be damaged. If the battery is not working, it may be best to consult with a LEVA trained technician, or other expert before charging.

Dealers, take a close look at the batteries you are receiving. Yes, they may have a sticker that warns you to not open the battery box at risk of voiding the warranty. And that should be respected – but at the same time you need an understanding of what is in there. If the supplier cannot show you a opened box, and will not answer questions in detail, maybe you should not be selling that battery. Once you can see it, look for a BMS, sturdy connections, and preferably, brand name cells.

A lithium ion electric bike battery pack with its cells exposed.

A lithium ion electric bike battery pack with its cells exposed.

Personally, I prefer 18650 cells (look like beefy AA cells) over pouch cells (look like aluminum foil envelopes). 18650s are mostly made by automation, and are usually made by the larger cell makers, who tend to have more stable product. I do not like to be told that a battery’s provence is “proprietary” or in any way secret, and I want to know who packaged the cells into a battery. A name that is only in Chinese, new to me, or from a company whose plant burned down a few years ago makes me more nervous than a packager that I have heard consistently good things about.

I would not buy a charger that does not have the output current info its label, and a UL listing (for the USA) or CE mark. And I prefer chargers and bikes / batteries that have connectors that simply do not fit anything except the correct items. This prevents many mistakes.

Ed Benjamin reviews the work members of the class who installed a Watts Up meter on a a ProdecoTech electric bike.

Ed Benjamin during a LEVA Technician Training at ProdecoTech.

Having a LEVA trained technician on the staff is a big step in the right direction.  The LEVA training examines battery issues and safety in detail, and such a technician will have a good understanding of how to prevent or deal with battery problems and fires.

No one in the ebike industry is taking any of this lightly.

Most industry execs would say that a fire that causes injury is a tragedy that they would do anything to prevent. And the execs in question are not only the brand managers, distributors, and dealers — this extends as well to the maker of the battery cells, the maker of the charger, and the battery assembler. Not to mention the insurers of all these entities.

So far as this writer knows, there have not been any injuries from fires that started with an ebike battery. If you know of one, please let me know. [email protected]

But there have been fires.

The litigious nature of the USA means that when an event occurs that may result in a lawsuit, everyone involved either wants to keep it quiet, or is ordered to keep it quiet by insurance companies, lawyers, and investors. So information can be scarce.

Not only are lawsuits a concern, but the news of such fires really dampens consumer and dealer confidence and results in reduced sales of electric bikes.

Working against this cloak of silence, in the USA, are the demands of the Consumer Product Safety Commission, which requires that hazardous consumer products be reported to the CPSC, an action that often results in a public recall of all of the affected products, as soon as a hazardous problem is identified.

Such a public acknowledgement of a problem can be a hard decision for an industry exec. And so some such reports are delayed or never made in hopes that the problem will be an isolated one and not repeated.  When a dealer or a consumer is aware of a problem that has not been reported, there is a mechanism at CPSC.GOV to report it yourself.

How to extinguish a Lithium Battery Fires:

One of the dangers of a lithium battery fire is that extinguishing it is not intuitive. If not carried through completely, the fire will re-ignite. A video on this can be found by going to youtube and searching for “FAA Lithium Fire.” The video you will find is intended to instruct air crew on extinguishing fires in laptops on board airplanes.

To put out a lithium battery fire:

  1. Use a fire extinguisher to quell the flames. This will often result in the fire being “out” and the battery simply smoking. Most fire extinguishers will accomplish this. But you are not done!
  2. Since lithium batteries will re-ignite if not cooled off, it is important to now cool the batteries with a generous amount of water. (NOT ICE) Keep the water coming.
  3. Best if the fire has been moved outside and the fire department called to deal with it.
  4. The smoke is bad. Avoid breathing it.

Bicycle Shop Battery Charging Rack:

Any electric bike shop will be safer if all batteries are always charged on a built-for-purpose-rack.

This rack should be on large, easy rolling wheels, and built of non flammable materials. And positioned near a doorway to the outside. With nothing to impede rolling the rack out the door.

In the event of a fire, a first reaction is to simply push or pull the rack to the outside.

On the rack are the batteries, the chargers, and a smoke detector. Only one extension cord to the rack, so that there is no interference when pushing it out the door. It should come unplugged easily from the motion of the rack being pushed out the door.

Use a timer on the power supply to the rack to prevent any charging during the night.

Have a 10 lb. or larger ABC and a Class D fire extinguisher handy.  Have access to a way to pour water on the fire once it is extinguished. (hose, bucket, water type extinguisher…)

Types of batteries used on ebikes, and their fire risk:

Sealed Valve Regulated Lead Acid (SVRLA): These look like the same batteries used for emergency lighting and computer Uninterruptible Power Supplies.  Overcharging one with a constant current (dumb charger) charger can cause an explosion and fire. Same problem that occurs with auto starter batteries on rare occasion.  What is happening is that outgassing of hydrogen occurs, which can, in some circumstances, result in an explosion. Unless the charger is quite powerful, this is pretty unlikely, even if left on charge for a long time.

NiCad batteries are really not used by the USA electric bike industry, and any found in Europe or Japan date back a number of years. Not usually regarded as flammable. But quite toxic and that is why they are no longer used in Europe or Japan.

NiMH batteries are also rare. But a few new bikes may have them, and a number of older bikes. Generally not flammable, but if shorted they can outgas hydrogen and this can cause an explosion if in a confined space.

Lithium Manganese (LiNiMnCoO2) are very widely used cells. These are very unlikely to burn when properly assembled and managed. But it is possible, especially with very cheap batteries or when abused. Most common problem is using the wrong charger for extended period of time. These are more compact than any of the other cells on this list and affordable. Thus they are popular for ebikes.

Lithium Iron Phosphate cells (LiFePO also called LFP and LIPO) are reputed to be the safest of the lithium cells. They do not burn easily, and the cases where they have done so are very rare indeed. These are bulkier than Lithium manganese, and somewhat limited  by this for ebike applications.

Lithium Cobalt (LiCoO2) is not used by any reputable company for ebike applications. Such cells are the best for energy density, and used in cell phones and other consumer electronic applications. But are not regarded as stable enough for large format batteries on ebikes. A common point of confusion is that some LiMa cells are described as Lithium Nickel Cobalt Manganese, and these are not the LiCo cells I am referring to.

Questions on electric bike batteries may be emailed to [email protected]

Mr. Benjamin made sure the class interacted with actually e-bikes.

Edward Benjamin instructing a LEVA Technician Training session at ProdecoTech.

Thanks to Edward Benjamin for his great tips on preventing electric bike battery fires!

P.S. Don’t forget to join the Electric Bike Report community for updates from the electric bike world, plus ebike riding and maintenance tips!

Comments

  1. says

    It’s a great article. Unfortunately there is no mention of the fact that many companies in our niche are shipping uncertified (UN 38.3) packs illegally. And many dealers are still buying uncertified packs from illegal shippers in China to sell to their customers.

  2. David Reeck says

    Thanks Ed,
    Very informative article.
    My take-away:
    Use only the eBike supplier’s original battery pack Charger.
    Only charge when the charger and battery pack can be monitored, or have a timer that will disconnect the power after about 4 hours of charging.
    Try to have cells that will provide an “open circuit” protection when the Cells are at too high a temperature.

    David Reeck (Master of Science in Electrical Engineering Control Systems, University of Colorado).

  3. David Reeck says

    Ed,
    The most desirable safety feature of a Battery Management System (within the Battery Pack) would continuously monitor BOTH the current (amperage) and the temperature of EACH cell. I believe the company “O2-Micro” has developed this type of BMS feature. And this data can be transmitted via BlueTooth to an external battery charger or other monitoring devices.

    Do you know which Battery Pack manufacturers use both current and temperature monitoring of each cell within the pack ?

  4. says

    David,

    You make some good points. My experience is that almost all BMS are designed to prevent over charge and over discharge, almost all will react to a short circuit, most will react to a thermal event, most have cell balancing features, and most monitor state-of-charge. To do these things, they do need to monitor cell voltage and the level of current coming in or out of the pack. But there must be dozens, if not more, of BMS designs. I am not familiar with the features on all of them.

    Ed

  5. says

    Jason,

    You raise an important issue. The distribution of el cheapo battery packs shipped under false documents to save money and usually misrepresented to the dealer and consumer is a real danger to consumers, dealers, and our industry. I think this practice is declining, but a responsible dealer should always report / complain to the shipping company when a mis represented battery arrives. It is not always the Chinese. I have seen a famous European battery packager mis label sample batteries to save money as well.

    • says

      Plenty of folks doing it right here in the US too Ed. Unfortunately a lot of people in the e-bike business (resellers and journalists alike) would rather keep quiet with their head in the sand instead of raising the issue and possibly ruffling feathers. Many sellers are also so price sensitive they would rather buy from cheap sources and not ask questions, instead of asking first and having to pay a premium for legitimate batteries and delivery.

      The fact is that buyers that accept illegal shipments are not liable. Dealers that know they’re buying non-certified (UN 38.3) batteries from sources that will definitely ship them illegally into the US don’t seem to mind as long as the price is low enough. What I hear often is “It’s okay because I’m not shipping them, all our customers are local.”.

      I think the solution is to educate everyone and especially the end buyers purchasing e-bike batteries (dealers and retail buyers). They need to be taught to ask first about certifications and return policies. Not only are the buyers accepting illegal shipments without reporting it (which they are legally required to do if hazmat certified themselves), but these packs also can never shipped back legally to the seller for warranty repair or replacement if there is an issue.

      Hopefully the industry will soon stop fearing the price of doing things right, get educated, and force those breaking the law for a profit to abide or leave. And hopefully that happens before one of these idiots has an issue that makes us all look bad.

  6. John Barous says

    Ed ,
    Excellent job !
    Your article is a great source of information for everyone.
    A must read for current eBike owners , those considering a eBike purchase and especially all retail shops selling eBikes.

    Although this segment is in it’s relative infancy we see a explosion
    (no pun intended) in intrest/popularity. Sales are increasing , with that there will be a tremendous need for a neutral information source.

    With all the new players in the eBike segment there will be a need
    not only to communicate but also to have some standardization.
    Years ago the bicycle industry had much in proprietary products (example Schwinn) that made sourcing replacements difficult for many.
    It would be great to shop your favorite reputable battery brand to fit
    any eBike.

    Although the dangers seem minor my hope is that the eBike companies
    will adequately inform the general public of any problems and recalls.
    As with all consumables, eBikes are transferred/sold to those other
    than the original purchaser with a even stronger need to know..

    Tip of the hat Ed in reminding us that we all can learn something new each day … Many Thanks !

    John Barous

  7. says

    I am of the opinion that the knowledge of the Battery pack regarding overcharging cut of voltage, current etc. is very important. The Dealer and manufacturer should educate the end user regarding these details. Ask him to monitor while charging even though BMS is connected. Manufacturers should provide good digital LCD voltage , current and charge monitors, so that end user can monitor the status of the Battery during Charge and discharge condition.
    This will definitely avoid false usage of Battery pack and avoid fire, miss use of the Battery.

    • says

      Yes. But as my wife observes, it is very difficult to get people to read directions, warnings, manuals, etc. She claims this is a problem primarily with males. I believe it is a universal human issue.

  8. Mike Calco says

    How interesting you would cover this subject matter at the very instance that Pedego recalled my battery acquired around June of 2012. It’s replacement should arrive here in the next couple of days. I had to provide proof that is was legally and properly disposed. I was told the reason was a fire hazard but not other details were shared.

    • says

      Mike, if you read my article, you would see that I am reacting to “a few recent stories in the media about fires that were caused by batteries on electric bicycles. Most of them at bike shops”. And if you were to search a bit, you would find that I, and others have been publishing articles on this issue for about 10 years. So this is not a new issue, new advice, or special for any brand. As for Pedego, I suggest that you ask them questions, as they would have more information on their batteries than anyone else.

  9. says

    I require all my batteries to have a bms level kill switch. this allows the battery to be turned into a collection of cells at will. Does not guarantee safety but i believe an important step.

    the battery is turned off during storage and shipping

  10. David Reeck says

    Hello Rafe,

    Like Ed, I cannot understand, specifically or electrically, what you meant to communicate.. My literal translation of what you said is that you can ISOLATE every battery cell, such that there are NO connections between any two cells within the battery pack. Interesting ! All battery packs will have some combination of cells in SERIES (which determine the pack overall voltage) and cells in PARALLEL (which determine the Amp-Hour rating of the pack). There are many potential methods to make these connections; simple methods and more complex methods.

    But, I cannot believe your words are what you intended to say, and cannot believe this is practical circuitry within a battery pack.
    Please help us to understand better.
    thanks.
    David

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