The battery is the essential power source for an electric bike, analogous to gasoline in a customary vehicle. It fuels not only the motor but also auxiliary features like integrated lights. The vast majority of ebikes utilize rechargeable lithium-ion (Li-ion) batteries, a technology that has become ubiquitous in portable electronics.

Photograph: adrienne So

High-quality Li-ion batteries offer a long lifespan, are relatively lightweight, and boast high energy density. However, poorly manufactured or untested batteries pose significant risks, including the potential for fires. The CPSC website (https://www.cpsc.gov/Safety-Education/Safety-education-Centers/Micromobility-Information-Center) provides up-to-date information on recalls and best practices for e-bike battery safety. Recent investigations by the New York City Fire Department (FDNY) have linked over 200 fires to e-bike batteries in 2023, resulting in over 150 injuries and 6 fatalities.

For a thorough understanding of Li-ion battery technology, the US Department of energy offers a detailed clarification (https://www.energy.gov/energysaver/articles/how-lithium-ion-batteries-work). Key to understanding these batteries is recognizing the distinction between energy density and power density.

Energy density, measured in watt-hours per kilogram (Wh/kg), indicates the amount of energy a battery can store. A typical e-bike battery might have an energy density of 150-250 Wh/kg. Power