21700 Cell

Referring to the 21 mm diameter by 70 mm length dimensions, 21700 cells are high-capacity, rechargeable lithium-ion battery cells. These cells offer up to 50% more capacity and improved energy density compared to traditional 18650 cells, providing longer run times. 21700 cells were popularized by electric vehicles (EVs), and are also used in power tools, consumer electronics, and energy storage systems.