Side-by-side comparison of Samsung INR18650-25R (18650) and Samsung INR21700-40T (21700)
| Samsung INR18650-25R | Samsung INR21700-40T | |
|---|---|---|
| Capacity | 2500 mAh | 4000 mAh |
| Nom. Voltage | 3.6 V | 3.6 V |
| Max Current | 20 A | 35 A |
| Weight | 43.8 g | 70 g |
| Energy | 9.0 Wh | 14.4 Wh |
| Energy Density | 205 Wh/kg | 206 Wh/kg |
| Form Factor | 18650 | 21700 |
| Typical R_int | 24.4 mOhm | 19.8 mOhm |
Showing 10A discharge rate for both cells
| Current | Samsung INR18650-25R | Samsung INR21700-40T |
|---|---|---|
| 0.5A | 24.4 | — |
| 0.8A | — | 19.8 |
| 2.5A | 22.2 | — |
| 4.0A | — | 17.1 |
| 5.0A | 21.0 | — |
| 10.0A | 21.0 | 17.1 |
| 15.0A | 20.4 | — |
| 20.0A | 20.4 | 16.6 |
| 25.0A | 19.9 | — |
| 35.0A | — | 16.2 |
Values in mΩ. Bold = lowest resistance at that current.
The Samsung 40T offers 60% more capacity (4000 vs 2500 mAh). The Samsung 40T supports higher continuous discharge (35A vs 20A), making it better for high-drain applications. The Samsung 25R is lighter at 43.8g. Note: these are different form factors (18650 vs 21700), so direct substitution is not possible without pack redesign.