When it comes to small flashlights, choosing the right rechargeable battery size¹ can make all the difference in brightness², runtime³, and convenience.

Different flashlight sizes⁴ demand different battery types⁵, and knowing the most common options helps you pick the right power source⁶.

In this article, I’ll walk you through the most popular rechargeable battery sizes⁷ used in small flashlights, their performance characteristics⁸, compatibility tips⁹, and which size is best for your specific needs.

Why Battery Size Matters in Small Flashlights?

The size of a rechargeable battery directly affects:

• 🔋 Runtime¹⁰ — how long your flashlight lasts on a charge
• ⚡ Power output¹¹ — how bright the beam can get
• 🧳 Portability¹² — how compact and pocket-friendly the flashlight is

Small flashlights need a delicate balance: compact enough to carry every day, but powerful enough to provide reliable light.

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Most Common Rechargeable Battery Sizes for Small Flashlights

1. AAA (Triple-A) Batteries

Size: 10.5mm diameter × 44.5mm length
Capacity: 800–1000 mAh (NiMH)
Chemistry: NiMH¹³ (rechargeable), Lithium (disposable)

Used In: Mini keychain flashlights¹⁴, penlights, ultra-compact EDC models

Pros:

• Lightweight and widely available
• Affordable rechargeable versions¹⁵ (NiMH)
• Low drain—great for basic flashlights

Cons:

• Short runtime
• Low voltage limits brightness

2. AA Batteries

Size: 14.5mm diameter × 50.5mm length
Capacity: 2000–2500 mAh (NiMH)

Used In: Medium-size flashlights¹⁶, utility lights, multi-use EDC models¹⁷

Pros:

• Excellent balance of size and capacity
• Long-lasting with good brightness
• Rechargeable NiMH versions are reliable and eco-friendly

Cons:

• Slightly bulkier than AAA
• Lower voltage than lithium-ion cells (1.2V vs 3.7V)

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3. 14500 Lithium-Ion Batteries

Size: Same as AA
Voltage: 3.7V (much higher than AA’s 1.2–1.5V)
Capacity: 600–1000 mAh

Used In: High-performance AA-sized flashlights with boosted brightness

Pros:

• High power output (good for tactical use)
• Fast charging
• Longer life cycles (300–500 charges)

Cons:

• Not compatible with all AA flashlights (can damage non-compatible models)
• Requires a protected circuit for safe use

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4. CR123A Rechargeable (16340)

Size: 17mm diameter × 34mm length
Voltage: 3.6–3.7V
Capacity: 600–800 mAh

Used In: Compact tactical flashlights, weapon-mounted lights

Pros:

• High voltage, bright performance
• Short and compact
• Fast charging available

Cons:

• Expensive compared to AA/AAA
• Shorter runtime due to small capacity

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5. 18650 Lithium-Ion Batteries

Size: 18.6mm diameter × 65mm length
Capacity: 2500–3500 mAh
Voltage: 3.6–3.7V

Used In: Larger compact flashlights with long runtime and strong beams

Pros:

• High capacity and brightness
• Long runtimes (ideal for heavy use or emergencies)
• Fast charging with USB-C or dedicated charger

Cons:

• Bulkier, not for ultra-compact lights
• Requires battery protection for safety

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Size Comparison Table

Battery Type	Size (mm)	Voltage	Capacity	Typical Use Cases
AAA (NiMH)	10.5 × 44.5	1.2V	~1000 mAh	Keychains, penlights
AA (NiMH)	14.5 × 50.5	1.2V	2000–2500 mAh	EDC, utility lights
14500 (Li-ion)	14.5 × 50.5	3.7V	~800 mAh	High-output compact lights
16340 (CR123A size)	17 × 34	3.6V	~700 mAh	Tactical flashlights, weapon lights
18650 (Li-ion)	18.6 × 65	3.6V	2500–3500 mAh	Heavy-duty flashlights, searchlights

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Which Size Should You Choose?

Here's a quick cheat sheet:

• ✅ For daily carry (EDC) → AAA or AA NiMH
• ✅ For higher brightness in compact size → 14500 or 16340
• ✅ For maximum runtime & power → 18650
• ⚠️ Check compatibility: Don’t use lithium-ion in a flashlight not rated for it.

Always verify your flashlight’s voltage and battery size requirements before inserting any cell.

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Charging Considerations

Most rechargeable batteries today come with convenient charging methods:

• NiMH (AAA/AA): Use standard AA/AAA smart chargers
• Li-ion (14500, 18650): Use protected chargers or USB-integrated batteries
• Built-in charging (USB-C/Micro-USB): Many flashlights now charge directly via USB

Look for overcharge protection and temperature monitoring to ensure safe charging.

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Final Thoughts

Small flashlights use a variety of rechargeable battery sizes—from the tiny AAA to the powerful 18650. Each size has trade-offs in size, brightness, and runtime.

Match your battery to your flashlight—and your usage style—for the best performance.

If you use your flashlight often, invest in a good set of rechargeable batteries and a quality charger. It’ll save money, reduce waste, and keep your light ready when you need it most.