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How does a charging e-bike battery pack respond when exposed to high or low environmental temperatures? Or when using third-party chargers? And, most importantly, how does that impact user safety?

In 2023, the Consumer Product Safety Commission (CPSC) tasked Ä¢¹½tv with testing several commercial e-bike battery packs to determine how they respond to edge-case charging conditions. The report describes our tests of five commercial e-bike battery packs and their chargers and the results of those tests, performed under four main scenarios:

• Increased environmental temperature while charging
• Decreased environmental temperature while charging
• Charging with out-of-specification currents
• Charging with out-of-specification input voltage

Our battery experts also examined the battery packs and cells before and after these tests and analyzed how weak points in the design and implementation of the products affected safety.

Safety considerations for e-bikes

Lithium-ion e-bike batteries pose a unique risk to consumers. If these battery packs experience thermal runaway events and catch fire, they are more difficult to extinguish than batteries in small consumer electronics. Many also lack the advanced monitoring, management, and safety systems found in electric vehicle battery packs. Understanding how e-bike batteries handle real-world charging conditions is key to making them safer for consumers and for helping industry organizations and regulators like the CPSC make informed decisions.

Our tests revealed that in several cases the battery pack battery management systems (BMS) allowed operation at temperatures outside of cell specification limits as well as accepted charge voltages in excess of specifications. Notably, one of the five battery packs failed to terminate charging after reaching the minimum charging current cut-off, which could possibly allow for overcharging. Many of the BMS shortcomings are likely to result in unintended degradation of the cells (e.g., lithium plating) that could eventually lead to problems like accelerated performance decay, internal short-circuiting, or, in extreme cases, thermal runaway.

These tests revealed the importance of a BMS that is fine-tuned to battery cell specifications and sophisticated enough to safely handle unintended usage profiles.

From the publication: "In electric micro-mobility products such as e-bikes, the extent of damage and hazard has been, regrettably, demonstrated through high-profile incidents. Due to the large size of the battery packs in e-bikes compared with other consumer electronic devices, a thermal failure can result in a substantial safety hazard that is difficult to contain."