The FR03 is a 1.5 volt AAA lithium cell using lithium iron disulfide chemistry, the same 10.5 by 44.5 mm size as a standard AAA. Energizer sells it as the L92 (Ultimate Lithium AAA). It swaps directly for an alkaline AAA and excels in high-drain, cold or set-and-forget devices.
FR03, side view, drawn to scale: 10.5 mm across, 44.5 mm tall.
Voltage
1.5 V
Size (D×H)
10.5 × 44.5 mm
Chemistry
Lithium iron disulfide (Li-FeS2)
Capacity
~1200 mAh
Same battery, other names
Every code below is the exact same cell as FR03. Any of them will fit and work identically.
FR6 / L91 (AA lithium): The AA version of the same 1.5 V lithium chemistry; larger case, more capacity, same advantages.
Buying and replacement notes
The FR03 (L92) matches the AAA alkaline (LR03) size and 1.5 V nominal, so it drops into any AAA device. It weighs less than half an alkaline AAA, runs from roughly -40 to 60 C, holds voltage under load, and keeps most of its charge for about 20 years. Those traits make it ideal for outdoor thermostats, sensors and headlamps that must work on the first try after months idle.
As with the AA lithium, a fresh AAA lithium reads near 1.8 V off-load, above an alkaline. The vast majority of AAA devices handle this without issue, but check the manual for anything that explicitly requires alkaline. Lithium AAA cells are single-use and must not be recharged.
Commonly used in
digital thermostatsoutdoor sensorsheadlampswireless keyboardsmedical devicesGPS units
⚠️ Keep away from children. Swallowed button batteries, especially 20 mm lithium coins, cause severe injury within hours. If a child swallows one, call the 24/7 National Battery Ingestion Hotline (US) at 800-498-8666 or poison control at 800-222-1222 immediately. What every parent should know.
Frequently asked questions
Is an FR03 the same as a AAA battery?
Yes, in size and voltage. The FR03 is a 1.5 V AAA cell at 10.5 by 44.5 mm, sold as the L92 or Energizer Ultimate Lithium AAA. It fits any AAA slot in place of an alkaline LR03. The chemistry is lithium iron disulfide rather than alkaline, giving it longer life under high drain and much better cold-weather performance.
When are lithium AAA batteries worth it?
When runtime, weight or reliability matter. Lithium AAA cells shine in high-drain gear, cold outdoor sensors and devices you rarely touch, because they hold voltage under load and keep their charge for years. For low-drain items like a TV remote, cheaper alkaline AAA cells are usually the sensible pick.
Can lithium AAA batteries replace alkaline AAA?
Yes. The FR03 (L92) is a direct swap for an alkaline AAA in nearly every device, matching the size and 1.5 V nominal. The only thing to watch is a rare voltage-sensitive device that specifies alkaline, since a fresh lithium AAA reads about 1.8 V off-load. Otherwise it works anywhere a AAA fits.
Are lithium AAA batteries rechargeable?
No. The FR03 is a primary, single-use cell and must not be recharged. For rechargeable AAA power, use NiMH cells, which run at 1.2 V and are a separate chemistry. Choose lithium AAA when you want the longest runtime and shelf life from a disposable battery, not repeated recharging.