18650 vs AA

An 18650 is a 3.6 V lithium-ion cell at 18 × 65 mm. An AA is a 1.5 V alkaline cell at 14.5 × 50.5 mm. Neither the size nor the voltage matches.

Last reviewed 10 September 2026

Quick answer

These are not alternatives. An 18650 is a rechargeable lithium-ion cell at 3.6 volts and is noticeably fatter and longer than an AA, so it will not fit an AA compartment. An AA is single-use alkaline at 1.5 volts. If you are looking for a rechargeable cell that fits an AA slot, the honest answer is a rechargeable NiMH AA at 1.2 V — not a lithium-ion cell.

Verdict:: Different size, different voltage, different job
Interchangeable:: no

Side-by-side specifications

18650 compared with AA
Specification	18650	AA
Chemistry	Li-ion	Alkaline
Type	Cylindrical	Cylindrical
Nominal voltage	3.6 V	1.5 V
Diameter	18 mm	14.5 mm
Height	65 mm	50.5 mm
Typical capacity	2000–3500 mAh	1800–2900 mAh
Rechargeable	Yes	No
Also sold as	INR18650, ICR18650, NCR18650	LR6, MN1500, AM3, R6

Size comparison

18650

Ø 18 mm · H 65 mm

Ø 14.5 mm · H 50.5 mm

These cells do not share a footprint, so one will not sit correctly in the other's compartment.

Size

18 × 65 mm against 14.5 × 50.5 mm. The 18650 is 3.5 mm wider and nearly 15 mm longer — it does not go in an AA bay.

Voltage

3.6 V against 1.5 V. Even if it fitted, it would feed a device more than twice what it expects.

What you probably want

For a rechargeable AA, the drop-in answer is NiMH at 1.2 V. It is slightly below alkaline voltage rather than far above it, which is why it works in ordinary devices.

Why the question gets asked

Usually by someone with a torch that takes both an 18650 and an AA via an adapter tube, or by someone looking for a rechargeable that will run an AA device. Those are two different questions with two different answers, and conflating them is how a 14500 ends up in a remote control.

If you want rechargeable AAs

NiMH at 1.2 V is the answer. It fits, it is safe in ordinary devices, and modern low-self-discharge cells hold their charge for a year. No lithium-ion cell is a drop-in replacement for an alkaline AA, whatever its shape.

If your torch lists both

Some lights accept one 18650 or one AA in an adapter, running dimmer on the AA because the driver has less voltage to work with. That is a designed-in option, stated by the manufacturer, and it is not evidence that the two cells are equivalent.

Can I use an AA instead of an 18650?

Not directly. The AA measures 14.5 × 50.5 mm against 18 × 65 mm for the 18650, so it will not seat properly in the same compartment.

18650 specs →AA 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.

18650 vs AA: common questions

Is the AA a direct replacement for the 18650?

What is the difference between the 18650 and the AA?

An 18650 is a 3.6 V lithium-ion cell at 18 × 65 mm. An AA is a 1.5 V alkaline cell at 14.5 × 50.5 mm. Neither the size nor the voltage matches. In short: different size, different voltage, different job.

Are the 18650 and the AA the same size?

No. The 18650 is 18 × 65 mm and the AA is 14.5 × 50.5 mm.

Which lasts longer, the 18650 or the AA?

The 18650. It is rated at 2000–3500 mAh against 1800–2900 mAh for the AA — roughly 1.2× the capacity, though real runtime depends on how much current your device draws.

Is the 18650 rechargeable?

Yes, and the AA is not. Never put a AA in a charger: single-use cells can vent, leak or catch fire when charged.