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18650 vs 21700
18650 and 21700 are not interchangeable. They differ in diameter (18 mm vs 21 mm), length (65 mm vs 70 mm). The 21700 holds about 1.5× the energy of the 18650 (4,500 mAh vs 3,000 mAh).
| 18650 | 21700 | |
|---|---|---|
| Type | rechargeable lithium-ion cell | rechargeable lithium-ion cell |
| Voltage | 3.6 V | 3.6 V |
| Size | 18 mm × 65 mm | 21 mm × 70 mm |
| Typical capacity | ≈ 3,000 mAh | ≈ 4,500 mAh |
| Rechargeable | yes | yes |
| Other codes | INR18650, ICR18650, NCR18650 | INR21700 |
Can I use 21700 instead of 18650?
No. Different width: 21 mm vs 18 mm.
Can I use 18650 instead of 21700?
No. Different width: 18 mm vs 21 mm.
Where each one is used
18650: high-power flashlights; power banks and laptop battery packs; e-bike and power-tool packs (as cells inside); vape mods.
21700: high-power flashlights; e-bike packs and power tools (as cells inside); vape mods.