What is equivalent to a FR6?

FR14505, L91, 15-LF, Energizer Ultimate Lithium AA, FR6/L91 — all the same 1.5 V cell under different manufacturer codes.

Can I use a 14500 instead of a FR6?

Also an AA-shaped lithium cell, but rechargeable lithium-ion at 3.7 V. The FR6 is a 1.5 V primary and a legitimate AA replacement; the 14500 is not.

Is the FR6 rechargeable?

No. It is a primary cell — charging one risks rupture or fire. Rechargeable look-alikes exist in the same size under different codes.

FR6 battery

What replaces a FR6

FR14505, L91, 15-LF, Energizer Ultimate Lithium AA, FR6/L91

1.5 V lithium (primary), 14.5 × 50.5 mm (diameter × height)

The FR6 is a single-use 1.5 V lithium (primary) cylindrical. The codes below are the same physical cell sold under different manufacturer names, and any of them will fit.

Specification

IEC designation: FR6
ANSI / NEDA: 15-LF
Nominal voltage: 1.5 V
Chemistry: Lithium (primary)
Size: 14.5 × 50.5 mm (diameter × height)
Typical capacity: 3000 mAh
Rechargeable: No — never charge it

Codes that mean the same battery

Different manufacturers, one physical battery. Voltage, chemistry and dimensions all match.
Code	Fits?
FR14505	Yes — same cell
L91	Yes — same cell
15-LF	Yes — same cell
Energizer Ultimate Lithium AA	Yes — same cell
FR6/L91	Yes — same cell

Codes that look close but are not

Code	Why it is not a substitute
14500	Also an AA-shaped lithium cell, but rechargeable lithium-ion at 3.7 V. The FR6 is a 1.5 V primary and a legitimate AA replacement; the 14500 is not.
LR6 alkaline	The FR6 replaces an alkaline AA in almost everything, but it holds a higher voltage under load, weighs a third less, and works to −40 °C. A handful of devices — some medical equipment and older cameras — are specified against it, and a very few chargers will attempt to charge it, which it must never be.

The FR6 is a primary cell and must never be put in a charger. Charging a sealed primary battery builds gas pressure inside a can with no vent designed for it, which is how they rupture or catch fire. Rechargeable look-alikes exist for several sizes and carry different codes — check the code, not the shape.

Where it turns up

Digital cameras and speedlights
Trail cameras left out over winter
GPS units and avalanche transceivers
Smoke alarms wanting a ten-year cell

Lithium/iron disulfide — the F prefix in IEC 60086. It is the only lithium chemistry that gives 1.5 V, which is what makes it a safe alkaline substitute where 3 V lithiums are not.

Common questions

What is equivalent to a FR6?: FR14505, L91, 15-LF, Energizer Ultimate Lithium AA, FR6/L91 — all the same 1.5 V cell under different manufacturer codes.
Can I use a 14500 instead of a FR6?: Also an AA-shaped lithium cell, but rechargeable lithium-ion at 3.7 V. The FR6 is a 1.5 V primary and a legitimate AA replacement; the 14500 is not.
Is the FR6 rechargeable?: No. It is a primary cell — charging one risks rupture or fire. Rechargeable look-alikes exist in the same size under different codes.

LR6 battery 1.5 V alkaline
LR03 battery 1.5 V alkaline
ICR18650 battery 3.6 V lithium-ion (rechargeable)
LR20 battery 1.5 V alkaline
HR6 battery 1.2 V nickel-metal hydride
LR14 battery 1.5 V alkaline
CR17345 battery 3 V lithium (primary)
HR03 battery 1.2 V nickel-metal hydride
8LR932 battery 12 V alkaline
INR21700 battery 3.6 V lithium-ion (rechargeable)
4LR44 battery 6 V alkaline
CR15H270 battery 3 V lithium (primary)

Sources

Official vendor product documentation — At One Place

How these figures are compiled and checked