18650 and 21700 are the two most common cylindrical lithium cells used in Citycoco battery packs, and their differences in size, capacity, energy density, discharge performance and service life directly determine the overall quality and use experience of the battery pack. Most low-cost Citycoco batteries on the market use 18650 cells, while high-end high-capacity long-life versions are basically equipped with 21700 cells. Understanding the cell differences can help users identify high-quality batteries and avoid being misled by inferior products.

In terms of basic specifications and capacity, the 18650 cell has a size of 18mm in diameter and 65mm in height, with a single-cell conventional capacity of 2000mAh to 3000mAh. It is a mature and mass-produced cell with low cost and wide compatibility. The 21700 cell is upgraded on the basis of 18650, with a size of 21mm in diameter and 70mm in height. The increased volume improves the single-cell capacity to 4000mAh to 5000mAh, and the single-cell energy density is increased by more than 35% compared with 18650. Under the same battery pack volume and weight, the battery pack assembled with 21700 cells has larger actual capacity and longer continuous endurance.

In terms of discharge performance and power stability, 21700 cells have obvious advantages. Citycoco scooters need instantaneous high-current discharge during starting and uphill riding. The 18650 cell has small single-cell capacity and limited discharge rate. When the motor outputs high power, it is prone to voltage drop, unstable power output, and serious heat generation. Long-term high-current discharge will accelerate cell aging. The 21700 cell has higher discharge rate, stronger current bearing capacity, more stable voltage output during high-power operation, lower heat generation, and better power continuity, which is more suitable for high-power Citycoco models above 1000W.

In terms of cycle life and safety, 21700 cells perform better. The optimized structural design of 21700 cells makes the internal electrode arrangement more reasonable, with lower internal resistance and smaller heat generation during charge and discharge. The cycle life can reach 1000 to 1500 times, while the cycle life of conventional 18650 cells is only 600 to 800 times. In terms of safety, 21700 cells have stronger explosion-proof and pressure-resistant capabilities, not easy to bulge and short circuit under extrusion and high-temperature conditions. The disadvantage is that the cost is higher. The overall price of 21700 battery packs is 20% to 30% higher than that of 18650 battery packs, which is the main reason why low-cost models still use 18650 cells.