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.

Quick answer

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

18650 compared with 26650
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

18650

Ø 18 mm · H 65 mm

26650

Ø 26 mm · H 65 mm

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.

Can I use a 26650 instead of a 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.

18650 specs →26650 specs →

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.

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