18650 and 21700 are named after their dimensions in millimetres. The 18650 is 18mm x 65mm; the 21700 is 21mm x 70mm. That small size difference changes a lot about how your pack performs.
Capacity and energy density
21700 cells typically store 4000-5000mAh versus 2500-3500mAh for 18650. For the same pack voltage, fewer 21700 cells deliver the same range, which simplifies wiring and spot-welding.
Current handling
21700 cells generally sustain higher continuous discharge, making them the better choice for high-drain applications such as scooters and power tools.
- Choose 18650 for compact builds and the widest cell selection
- Choose 21700 for maximum range and high current
- Never mix formats or brands inside one pack
Both formats spot-weld the same way with pure-nickel strip. NexEV stocks holders and nickel for both — see the shop for current options.
