18650 vs 26650
Both 3.6 V lithium-ion. At 26 × 65 mm the 26650 is far wider than the 18 × 65 mm 18650 and holds close to double the charge.
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Both are rechargeable lithium-ion at 3.6 volts. The 26650 is much fatter — 26 mm across against 18 — and holds close to double the energy. They do not interchange in either direction. The 26650 turns up mostly in large torches and solar storage; most equipment is built around the 18650.
- Verdict:
- 26650 for capacity, but far fewer devices take one
- Interchangeable:
- no
Side-by-side specifications
| Specification | 18650 | 26650 |
|---|---|---|
| Chemistry | Li-ion | Li-ion |
| Type | Cylindrical | Cylindrical |
| Nominal voltage | 3.6 V | 3.6 V |
| Diameter | 18 mm | 26 mm |
| Height | 65 mm | 65 mm |
| Typical capacity | 2000–3500 mAh | 4000–5500 mAh |
| Rechargeable | Yes | Yes |
| Also sold as | INR18650, ICR18650, NCR18650 | INR26650, IMR26650 |
Size comparison
These cells do not share a footprint, so one will not sit correctly in the other's compartment.
Same length, different width
Both are 65 mm long. The 26650 is 8 mm wider, and that is the whole difference — an 18650 in a 26650 tube will not hold contact.
Capacity
4000–5500 mAh against 2000–3500 mAh, roughly double for a cell that takes up roughly double the volume.
Why the 18650 won
Packs are built from many cells, and the 18650 packs more efficiently and costs less per unit of capacity. The 26650 survives where a single large cell is simpler than several small ones.
Why packs favour the narrower cell
Cylinders leave gaps when packed together, and the smaller the cylinder the less space is wasted relative to the whole. The 18650 also had two decades of volume manufacturing behind it, so it is cheaper per unit of capacity even where a 26650 would fit.
Where a single large cell wins
One 26650 means one cell to charge, monitor and balance. For a torch or a small solar setup, that simplicity is worth more than packing efficiency, which is the niche the size still occupies.
Availability is narrowing
Fewer manufacturers build 26650s each year and the good ones can be hard to source. If you own equipment built around them it is worth knowing that replacements may get harder to find rather than easier.
Can I use a 26650 instead of an 18650?
Not directly. The 26650 measures 26 × 65 mm against 18 × 65 mm for the 18650, so it will not seat properly in the same compartment.
Check before you swap. Batteries with similar dimensions are not always interchangeable. Always verify voltage, chemistry and the requirements printed in your device manual before fitting a replacement.
18650 vs 26650: common questions
Is the 26650 a direct replacement for the 18650?
Both are rechargeable lithium-ion at 3.6 volts. The 26650 is much fatter — 26 mm across against 18 — and holds close to double the energy. They do not interchange in either direction. The 26650 turns up mostly in large torches and solar storage; most equipment is built around the 18650.
What is the difference between the 18650 and the 26650?
Both 3.6 V lithium-ion. At 26 × 65 mm the 26650 is far wider than the 18 × 65 mm 18650 and holds close to double the charge. In short: 26650 for capacity, but far fewer devices take one.
Are the 18650 and the 26650 the same size?
No. The 18650 is 18 × 65 mm and the 26650 is 26 × 65 mm.
Which lasts longer, the 18650 or the 26650?
The 26650. It is rated at 4000–5500 mAh against 2000–3500 mAh for the 18650 — roughly 1.7× the capacity, though real runtime depends on how much current your device draws.
Background reading
The wider questions behind these two codes.