16340 Batteries (RCR123A): How to Choose the Right One

16340 batteries are compact, rechargeable lithium cells sized 16 x 34 mm. Also known as RCR123A, they are commonly used in small, high-output flashlights, optics/IR illuminators, and specialty gear that is explicitly rated for rechargeables. This guide explains which 16340 to pick, when to avoid them, and how to charge and care for them safely.

What is a 16340 Battery?

• Size: ~16 mm diameter x ~34 mm length (protected cells can run 34–36 mm).
• Chemistry options:
  • Li-ion 3.6/3.7 V nominal (4.2 V full): highest output; most common.
  • LiFePO4 3.2 V nominal (3.6–3.65 V full): closer to CR123A voltage; lower capacity.
• Typical capacity: 500–900 mAh depending on chemistry and protection/USB features.

Can I replace a CR123A with a 16340?

Sometimes. A CR123A primary cell is 3.0 V nominal (about 3.2 V fresh). A 16340 Li-ion charges to 4.2 V, which can damage devices not designed for rechargeables. Only use a 16340 if the manual or manufacturer states compatibility with “RCR123A” or rechargeable 16340 cells. When in doubt, stay with CR123A primaries or use LiFePO4 3.2 V only if the device allows it.

Key Choices and How to Decide

1) Voltage & Chemistry

• 3.7 V Li‑ion: Best for high-brightness lights rated for RCR123A. Highest output and capacity. Requires a 4.2 V Li‑ion charger.
• 3.2 V LiFePO4: Safer voltage for some devices that dislike 4.2 V peaks. Lower capacity. Requires a 3.6/3.65 V LiFePO4 charger.

2) Protection Circuit

• Protected: Built‑in over‑charge/over‑discharge/short‑circuit protection. Slightly longer. Recommended for most users and single‑cell flashlights.
• Unprotected: Maximum current and smallest size but no internal safeguards. For experienced users with devices that provide their own protection.

3) Top Style & Fit

• Button‑top is often required for flashlights and devices with recessed contacts.
• Flat‑top may work in spring‑loaded bays. Check that overall length fits (some protected/USB cells are 1–2 mm longer).

4) Capacity & Discharge

• Capacity: Higher mAh = longer runtime but may come with lower max discharge. Typical range 500–900 mAh.
• Max continuous discharge: Match the cell’s rating to your device draw; many 16340s support roughly 2–6 A. Check your light’s specs.

5) Charging Convenience

• Standard cells: Use a compatible external charger—most flexible and often higher capacity.
• USB‑rechargeable cells: Charge via micro‑USB/USB‑C built into the cell; convenient but can reduce capacity slightly.

Runtime: Quick Estimates

Approximate runtime (ignore driver losses): runtime (hours) ≈ capacity (mAh) ÷ draw (mA).

• Low mode 200 mA with a 700 mAh cell ≈ 3.5 hours.
• Medium 500 mA ≈ 1.4 hours.
• High 1.5 A (1500 mA) ≈ 0.47 hours (~28 minutes). Actual turbo modes may step down for heat.

When to Use vs. Avoid

Use 16340 if:

• Your flashlight or device explicitly supports “RCR123A/16340”.
• You need high output in a very small form factor.
• You prefer rechargeable convenience over primary cell shelf life.

Avoid or reconsider if:

• Your device manual specifies “3.0 V CR123A only”.
• The device runs two CR123A in series and is not rated for two 16340 (8.4 V max).
• You need multi‑year standby in cold climates (CR123A primaries perform better for alarms/sensors).
• You need longer runtime than a 16340 can provide—consider 18350 or 18650 where supported.

Alternatives at a Glance

Cell	Nominal V	Typical Capacity	Best for
CR123A (primary)	3.0 V	1400–1700 mAh (non‑rechargeable)	Long shelf life, low‑drain sensors, cold weather
16340 Li‑ion (RCR123A)	3.6/3.7 V	500–900 mAh	Compact, high‑output lights rated for rechargeables
16340 LiFePO4	3.2 V	300–600 mAh	Devices sensitive to high voltage (if allowed)
18350 Li‑ion	3.6/3.7 V	800–1200 mAh	More runtime if device fits 18 x 35 mm

Charging & Care

• Use the correct charger: Li‑ion 16340 charges to 4.2 V (CC/CV). LiFePO4 needs a 3.6/3.65 V charger. Do not mix chemistries or chargers.
• Charge rate: 0.3–0.5 C is gentle (e.g., 300–500 mA for a 700 mAh cell). Avoid fast charging unless the cell explicitly supports it.
• Storage: Store at ~40–60% charge in a cool, dry place; top up every 3–6 months.
• Cycle life: Typically ~300–500 full cycles with proper care.

Safety Notes

• Prefer protected cells for general use. Never carry loose cells—use a case.
• Do not short, crush, or expose to heat. Replace cells that swell, vent, or are physically damaged.
• Do not use multiple 16340s in series unless the device is rated for the higher voltage.
• Do not mix old and new cells or different brands/capacities in the same device.

FAQ

What’s the difference between 16340 and RCR123A?

They refer to the same rechargeable size. “16340” describes dimensions (16 x 34 mm). “RCR123A” indicates a rechargeable version of the CR123A form factor.

Can I use a 16340 in place of a CR123A?

Only if the device supports rechargeables or explicitly states RCR123A compatibility. A 3.7 V Li‑ion 16340 reaches 4.2 V when full, which can damage 3.0 V‑only devices. If allowed, LiFePO4 (3.2 V) may be safer, but confirm in the manual.

Should I choose protected or unprotected?

Protected cells are recommended for most users and single‑cell flashlights. Unprotected cells are for advanced users with gear that provides its own protection and requires maximum current/shorter length.

How long will a 16340 run my light?

As a rough guide, a 700 mAh cell at 500 mA runs ~1.4 hours; at 1.5 A, ~25–30 minutes before step‑downs. Actual runtime depends on the light’s driver and thermal limits.

What charger do I need?

Use a quality Li‑ion charger set for 4.2 V for standard 3.7 V cells. For LiFePO4 3.2 V cells, use a charger with a dedicated 3.6/3.65 V mode. Never charge LiFePO4 with a 4.2 V Li‑ion program.