By Jonathan Jordan

The continued growth of e‑bike adoption has been accompanied by risks related to lithium‑ion batteries, including fires and explosions. While relatively infrequent, such events may present significant risk exposure due to the severity of damage and the complexity of causation. In March of this year, the CPSC issued a warning to buyers of a particular e-bike that the e-bikes’ batteries and wires could ignite, posing a fire hazard to consumers.[1] Over a six-year period, the CPSC reported 14 fatalities related to eight incidents of lithium-ion battery fires involving e-bikes.[2] Cities such as New York have implemented plans to promote safe electric micromobility usage and to regulate lithium-ion batteries sold in New York City and strengthen fire safety related to battery fires.[3]

Recent developments in incident data, standards, and litigation trends suggest several important considerations for manufacturers, distributors, insurers, and counsel.

1. Causation

Some e‑bike battery failures involve thermal runaway, a mechanism in which a battery cell overheats and triggers a cascading reaction across the pack. In these events, an initial increase in temperature — whether caused by an internal defect, physical damage, misuse/abuse, or a charging-related issue — initiates a series of chemical reactions that generate heat faster than the battery can dissipate it. As that heat builds, it destabilizes the internal components of the cell, including the separator and electrolyte, leading to further heat generation in a self‑reinforcing cycle. Once a single cell enters this state, the heat, gases, and ejecta released can quickly spread to adjacent cells, creating a chain reaction that propagates throughout the battery pack. This rapid escalation can cause the battery to vent flammable gases, ignite, or even explode, and because the process is self‑sustaining, it is extremely difficult to stop once it begins.

However, thermal runaway is not itself a root cause, but rather the result of a short-circuit brought on by various potential causes, such as a manufacturing defect, pack and/or system-level design limitations like inadequate battery management or thermal controls, misuse or abuse by the end-user(s), improper environment usage, and charging-related conditions such as the use of incompatible or defective chargers. Additional contributors may include physical damage to the battery over time, as well as the use of low-tier, aftermarket, and/or uncertified components that introduce poor quality, poor design, or variability into system performance and safety.

2. User Conduct

Certain e‑bike charging and usage practices are known to increase risk, including charging batteries in inappropriate environments (e.g., damp, wet), non-OEM or uncertified battery replacement, and misuse and/or abuse such as battery pack disassembly or physical damage. These types of behaviors may support arguments related to comparative fault, product misuse, or a break in the causal chain. Real-world market responses reflect these concerns. For example, in 2023, Amazon discontinued sales of certain third‑party batteries in New York City following a cease‑and‑desist order tied to concerns about uncertified products and safety compliance.[4] Against this backdrop, early investigation into the actual conditions of use is critical and can materially influence the assessment and management of liability exposure.

3. Standards Compliance

Recent developments in e-bike safety have been driven by a shift in how standards address risk. The industry is moving toward system-level certification, not just evaluation of individual components in isolation. Most notably,  UL 2849 assesses the interaction between the battery, charger, motor, and control systems. This reflects a growing recognition that failures could occur not only within a single component, but at the interfaces between them, particularly under real-world stress conditions such as overcharging, mechanical shock, or environmental exposure.

Equally significant is the expanding focus on aftermarket components and lifecycle risk. Some reported incidents[5] have been associated with third-party batteries, chargers, or modifications that fall outside established certification frameworks, prompting regulators, retailers, and insurers to tighten controls around uncertified products. This has elevated the importance of not only initial product compliance, but also downstream use and modification. In practice, this means that compliance is no longer a static, point-in-time consideration; it is a dynamic factor that touches product design, supply chain integrity, user behavior, and post-sale component replacement, all of which can influence both safety outcomes and the allocation of liability.

4. Supply Chain Complexity

E‑bike systems often involve multiple parties across the supply chain, including battery cell manufacturers, pack assemblers, charger manufacturers, OEMs, and retailers. As a result, a failure could be attributable to the interaction of components designed, manufactured, and integrated by different entities within the system rather than a single point of failure. In practice, each component plays a role in maintaining safe operating conditions. If these elements do not operate in harmony as intended, the system could move outside its safe operating envelope, even if each individual component appears compliant in isolation.

These interactions can complicate causation because failure mechanisms can be distributed rather than discrete. A battery may degrade over time due to subtle manufacturing variability, but that degradation may only manifest as a failure when combined with a particular charging pattern, environmental condition, or system configuration.

5. Evidence Preservation and Early Analysis Are Critical

Battery incidents often damage or destroy key physical evidence due to the extreme heat involved and the rapid progression of fire events. In many cases, critical components such as battery packs, chargers, and internal cell structures are severely degraded or entirely consumed, limiting the ability to conduct direct forensic examination after the fact. As a result, causation analysis frequently relies on indirect evidence, including the charging setup, the surrounding environment, and the history of how the product was used or maintained.

Given these constraints, early documentation and preservation efforts are essential, as even seemingly minor details can become significant in reconstructing the sequence of events. Investigators and experts are typically required to evaluate potential failure modes and systematically eliminate alternative causes based on the available evidence. In practice, timely scene preservation and early expert engagement are often determinative in developing a clear, defensible causation narrative.

Conclusions

Taken together, these considerations underscore that organizations involved in the design, manufacturing, distribution, or underwriting of e‑bike products should take a proactive and integrated approach to risk management. This includes ensuring that product design and documentation adequately address foreseeable misuse scenarios, particularly with respect to charging, usage, and replacement components, while also maintaining clear and well-documented compliance with evolving safety standards such as UL 2849. At the same time, attention to supply chain controls remains critical, particularly where third-party or aftermarket components may introduce additional variability and risk.

Equally important are well-developed incident response protocols that prioritize rapid investigation, thorough documentation, and timely evidence preservation, all of which can be outcome-determinative in litigation. Ultimately, e‑bike battery investigations reflect a broader shift in product liability toward system-level risk, where outcomes can be driven by the interaction of design, usage, and supply chain variables rather than isolated defects.

How Secretariat Can Assist

Whether it’s alkaline, lithium-ion, nickel-metal hydride, or lead-acid batteries, each chemistry comes with its own unique performance characteristics and use cases. At Secretariat, our engineering consultants provide expert support across the entire battery product lifecycle, from design and manufacturing to deployment, diagnostics, and end-of-life considerations. With hands-on experience in both the production and real-world application of batteries, our team brings deep technical insight into battery performance, safety, failure analysis, and quality assurance.

[1] CPSC Warns Consumers to Immediately Stop Using Ridstar E-Bikes Due to Fire Hazard; Risk of Serious Injury or Death | CPSC.gov

[2] Micromobility Products-Related Deaths Injuries and Hazard Patterns 2017-2021

[3] Mayor Adams Announces Plan to Combat Lithium-Ion Battery Fires, Promote Safe Electric Micromobility Usage – NYC Mayor’s Office

[4] Amazon Stops Selling Illegal Batteries After City Cease-and-Desist Letter – Streetsblog New York City, Amazon Is No Longer Selling Illegal E-bike Batteries to New Yorkers. Finally.

[5] Nearly half of e-bike fires in 2024 linked to post-market conversions