In 1870, biologist Thomas Henry Huxley delivered a speech in which he said “The great tragedy of science—the slaying of a beautiful hypothesis by an ugly fact.” It has since been altered by many to a “beautiful theory,” but the core remains—many of our most reasonable, believable, and elegant conjectures are simply not consistent with reality. 

So, you may be asking yourself, “what point am I getting at here?” Well, one of the benefits of leading this E-bike Battery Safety Project is that I get to talk with a lot of people about the issues we’re facing with e-bike fires, and each seems to have a different idea of what may be causing them. I’m going to list a few here, starting with the incredible (read: “not credible”) to those more likely to be grounded in reality. But the whole point of this project is to serve up some ugly facts, like British blood pudding—quite ugly but serviceable for the purpose—to help us discern which of the beautiful theories are the ones we should be acting upon.

Here is a short list of beautiful theories:

• “The batteries aren’t certified.” Simply not true. All the cells will be certified to UN 38.3, and most if not all of them also be certified to UL1642. At which point the discussion degrades into certification-alphabet-soup—experts reply that those certifications aren’t enough, and that another certification exists that is not being used broadly. While these points are true enough, there isn’t any evidence that the certifications matter, or even that the fires are caused more frequently by uncertified vs certified batteries.
• “It’s the De Minimis Value imports.” In the US, express shipments that cost less than $800 are not subject to duty or inspection. Which is why there are tons of e-bikes for sale on Amazon for $799. I have one in my garage from Walmart for about the same price. However, our survey showed only 9% spending less than $1000. Perhaps all the fires come from those 9%. We’ll learn more as we dig in more closely.
• “Cheap Chinese imports.” In fact, most e-bikes are made in China, even many sold by US or European brands. Many quality products are manufactured in China, so we think it will have more to do with the design and manufacturing quality than the country of origin.
• “Non-OEM replacement batteries.” Many bikes will take a replacement battery, and many owners will own two or more batteries, sometimes just to extend the range of riding in a single day without recharging. This one is possible, and so we have purchased several non-OEM batteries to compare to the OEM batteries. We shall see which is more important.
• “Rebuilt batteries.” E-bike batteries can, and often are, rebuilt (here is a friendly guide on how to do it). And my guess is that there are a lot of DIYers who will cut corners. With an abundance of information on YouTube and other outlets, this could very well be a possible culprit. In our survey, there was a significant positive response indicating ownership of refurbished batteries.
• “There is no BMS.” It’s possible that there is no BMS, but even more likely there is one. However, it may have active or passive balancing, may or may not have temperature sensors, etc. This is another detail that we will dig into as we disassemble the batteries.
• “The batteries are not designed for the abuse they see.” Likely the range of abuse that e-bike batteries go through is quite varied, from a gentle commute to a rugged off-roader, to hurried delivery people dropping and tossing the bikes. The answer will be in the details of seals, welds, wire gauges, case thicknesses and others. We will get a better handle on this as we disassemble used packs—are the wear points in places where they could cause potential danger?
• “The chargers are overloading circuits.” I had a report of a bike shop with 20 chargers plugged into a single outlet, which certainly wouldn’t be safe. But likely the building circuit protectors would trip before anything terrible happened—that’s what they are designed for. It’s no less safe than plugging too many of anything into a single plug, which every teenager with a stereo has done at some point.
• “The cell monitoring wires cause sparks.” CIf one breaks loose, or if another metal piece comes close to it, there can be a spark. It won’t matter, however, unless there is something to ignite. We’ll be able to tell a lot by looking at the state of the connections in a used pack. If there are a bunch of wires no longer connected, it could also mean the cells are no longer properly balanced, which could lead to overcharging or over-discharging. This may be a real danger signal, and only the used packs will tell us the truth.
• “One cell leaks, hydrogen accumulates, and is later ignited.” Some friends have suggested this for the Alabama truck explosion, where the sides of the trailer were blown off. This can happen if one or more cells gases without burning, accumulating flammable gas in a closed container. Could this happen with an e-bike? It’s likely only if it were stored in a closed container. There likely isn’t enough gas space inside the battery itself to contain enough hydrogen for an explosion. But in a closet or small room? Absolutely.
• “Non-OEM chargers are allowing overcharge.” While most chargers are made to handle many situations, if the BMS of the battery is getting something it isn’t designed to handle, there certainly could be some troubles related to potentially overcharging the battery.
• “The BMS has no disconnect switch.” One key feature for a BMS is a way to do a hard disconnect from the load—which is the bike. If there is no relay or hard switch controlled by the BMS, then it’s possible that the battery could be strained beyond its design point. This could be especially true if there are no temperature sensors connected to the BMS. Hot and overloaded is not a good combination.

Two weeks ago, I had the opportunity to introduce the project to Sandy Munro, from Munro Live, who was very enthusiastic about the importance of what we are working on. He even asked one of his top engineers, Tom Prucha, to support us. Tom has been a great resource, and his experience helping to disassemble fully electric vehicles will prove invaluable as we try to decipher the clues that are contained in the new and used e-bike batteries, and the data we get from the field. 

This is an important project. The death count in New York City so far this year is seven, already eclipsing last year. While it’s a small number compared to the Ukraine and other global conflicts, each death is a person’s life taken too soon. If it can be preventable, then it’s what we are out to do.