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eAntriebstechnik, eBike, Wartung & Reparatur

Electric Bike Battery Fires and How to Prevent Them


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

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.

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.

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. ed@LEVAssociation.com

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 toed@levassociation.com