21700 vs 18650 Battery The 21700 and 18650 refer to sizes of lithium-ion battery cells. The 18650 measures 18mm x 65mm and typically has capacities between 1800mAh to 3500mAh, used in laptops and earlier Tesla models. The larger 21700 measures 21mm x 70mm, offers capacities from 3000mAh to over 5000mAh, and is used in newer electric vehicles, like Tesla's Model 3. While the 21700 provides more energy storage due to its size, the choice between them depends on application requirements, such as space, energy needs, and cost. Both can be designed for various discharge rates, and their lifespans depend on specific cell designs.