Flashlight Battery Size: Types, Choosing Tips and FAQs

By Ufine, Updated on May 10, 2024

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Choosing the right flashlight battery size can be overwhelming, as many different flashlight battery types and sizes are available. Whether looking for the best rechargeable flashlight battery or comparing 18650 vs 26650 batteries, understanding which type best suits your flashlight can significantly improve its performance. In this detailed guide, we’ll explore various flashlight battery types and sizes and provide expert tips for choosing the best flashlight battery for your specific needs.

When searching for flashlight battery sizes, users typically need to:

Identify physical dimensions for battery replacement
Compare capacities of different sizes (e.g. 18650 vs 26650)
Find compatible sizes for specific flashlight models

This guide provides detailed size comparison charts, real-world usage examples, and a step-by-step measurement method to solve these core needs.

Part 1. Understanding flashlight battery sizes and types

Flashlight batteries come in three primary categories: Lithium Batteries, NiMH Batteries, and Other types. Each type offers distinct advantages and is suitable for different applications.

Lithium Batteries: Known for their high energy density and long shelf life, lithium batteries are a popular choice for flashlights. They come in various sizes, including 18650, 26650, 21700, and more.
NiMH Batteries: Nickel-metal hydride batteries are rechargeable and offer a cost-effective solution for flashlight users. Standard sizes include AA, AAA, C, D, and 9V block batteries.
Other types of flashlight batteries: This category includes alternative battery options such as 6V and 12V block batteries and the smaller 4LR44, also known as AG13.

Part 2. Flashlight battery size comparison chart

Battery Size	Diameter (mm)	Length (mm)	Voltage (V)	Capacity Range	Best For
18650	18	65	3.7	2500-3500mAh	Tactical flashlights
26650	26	65	3.7	4000-5000mAh	Search lights
21700	21	70	3.7	3500-4500mAh	EDC lights
16340 (CR123A)	16	34	3.0-3.7	600-1000mAh	Compact flashlights
14500	14	50	3.7	600-1000mAh	Mini flashlights
AA	14.5	50.5	1.2-1.5	2000-3000mAh	Household flashlights
AAA	10.5	44.5	1.2-1.5	600-1000mAh	Headlamps
CR2	15.6	27	3.0-3.2	600-900mAh	Specialty lights
D Cell	34.2	61.5	1.2-1.5	5000-10000mAh	Lanterns

Pro Tip: Always measure your battery compartment with calipers. Most flashlights allow 0.5mm size tolerance.

Part 3. Detailed breakdown of flashlight battery sizes

Lithium Batteries:

18650 battery

Specifications: The popular 18650 battery size (18mm × 65mm), with a voltage of 3.7V and a capacity typically ranging from 2500mAh to 3500mAh.
Features: 18650 batteries, known for their high energy density and long lifespan, are ideal for high-performance flashlights.
Suitability: Ideal for tactical flashlights, high-powered LED flashlights, and other devices requiring long runtime and high output.

26650 battery

Specifications: The 26650 battery is more extensive, with a diameter of 26mm and a length of 65mm, offering a voltage of 3.7V and a capacity typically ranging from 4000mAh to 5000mAh.
Features: These batteries provide higher capacity and longer runtime, making them suitable for heavy-duty flashlights.
Suitability: Commonly used in searchlights, high-lumen flashlights, and powerful handheld spotlights for outdoor activities.

21700 battery

Specifications: The 21700 battery measures 21mm in diameter and 70mm in length, with a voltage of 3.7V and a capacity typically ranging from 3500mAh to 4500mAh.
Features: 21700 batteries, which balance capacity and performance, are increasingly popular in modern flashlight designs.
Suitability: It is suitable for everyday carry (EDC) lights, bike lights, and tactical flashlights requiring a smaller form factor.

16340 (CR123A) battery

Specifications: The 16340 battery, also known as CR123A, has a diameter of 16mm and a length of 34mm. Its voltage typically ranges from 3.0V to 3.7V, and its capacity varies from 600mAh to 1000mAh.
Features: CR123A batteries offer high voltage and excellent shelf life, making them ideal for devices requiring long-term storage or infrequent use.
Suitability: Commonly used in compact flashlights, weapon-mounted lights, and surveillance cameras due to their small size and high energy output.

14500 battery

Specifications: The 14500 battery has a diameter of 14mm and a length of 50mm. It provides a voltage of 3.7V and a capacity typically ranging from 600mAh to 1000mAh.
Features: Similar in size to AA batteries, 14500 lithium batteries offer higher voltage and energy density, making them suitable for compact flashlights with demanding power requirements.
Suitability: Ideal for mini flashlights, penlights, and keychain lights where space is limited but performance is essential.

18350 battery

Specifications: The 18350 battery has a diameter of 18mm and a length of 35mm. Its voltage is 3.7V, and its capacity typically ranges from 800mAh to 1200mAh.
Features: Despite their shorter length, 18350 batteries offer decent capacity and power output, making them suitable for compact flashlight designs without sacrificing performance.
Suitability: Commonly used in small and medium-sized flashlights, especially those requiring a shorter form factor for portability or concealment.

10180 battery

Specifications: The 10180 battery is ultra-compact, measuring 10mm in diameter and 18mm in length, with a voltage of 3.7V and a capacity typically ranging from 70mAh to 120mAh.
Features: Despite their small size, 10180 batteries offer compactness and convenience. They are suitable for micro flashlights and keychain lights where space is limited.
Suitability: This material is suitable for pocket-sized flashlights, emergency lights, and keychain flashlights where space is limited but occasional use is expected.

CR2 battery

Specifications: CR2 batteries have a diameter of 15.6mm and a length of 27mm. Their voltage typically ranges from 3.0V to 3.2V, and their capacity varies from 600mAh to 900mAh.
Features: CR2 batteries offer a combination of small size and decent capacity, making them suitable for specific flashlight designs.
Suitability: Commonly used in laser pointers, digital cameras, and specific types of flashlights requiring a compact yet powerful energy source.

CR2450 battery

Specifications: CR2450 batteries are coin cell batteries with a diameter of 24.5mm and a thickness of 5mm. They provide a voltage of 3.0V and a capacity typically ranging from 600mAh to 700mAh.
Features: Despite their small size, CR2450 batteries offer sufficient capacity for specific flashlight applications.
Suitability: Occasionally used in speciality flashlights, keychain lights, and electronic devices where space is limited and power consumption is relatively low.

NiMH Batteries:

AA (HR6) battery

Specifications: AA batteries have a diameter of 14.5mm and a length of 50.5mm, provide a voltage of 1.2V, and typically have a capacity ranging from 2000mAh to 3000mAh.
Features: NiMH AA batteries are rechargeable and offer good capacity and performance, making them a cost-effective and eco-friendly choice for flashlight users.
Suitability: It is suitable for a wide range of flashlight models, including everyday carry lights, camping lanterns, and household flashlights requiring AA batteries.

AAA (HR03) battery

Specifications: AAA batteries have a diameter of 10.5mm and a length of 44.5mm, providing a voltage of 1.2V and a capacity typically ranging from 600mAh to 1000mAh.
Features: AAA batteries are minor compared to AA batteries but offer similar performance and compatibility with rechargeable NiMH technology, making them suitable for compact flashlight designs.
Suitability: Commonly used in mini flashlights, headlamps, and small electronic devices where limited space and lightweight power sources are required.

C (HR14) battery

Specifications: C batteries have a diameter of 26.2mm and a length of 50mm, providing a voltage of 1.2V and a capacity typically ranging from 2500mAh to 4500mAh.
Features: NiMH C batteries offer higher capacity and longer runtime than AA and AAA batteries, making them suitable for larger flashlights and devices with higher power requirements.
Suitability: It is ideal for heavy-duty flashlights, camping lanterns, and emergency lights where long-term use and reliability are essential.

D (HR20) battery

Specifications: D batteries have a diameter of 34.2mm and a length of 61.5mm. They provide a voltage of 1.2V and a capacity typically ranging from 5000mAh to 10000mAh.
Features: D batteries are the largest among standard NiMH batteries. They offer the highest capacity and longest runtime, making them suitable for high-power flashlights and devices requiring sustained energy output.
Suitability: Commonly used in industrial flashlights, emergency lighting systems, and outdoor lanterns where durability and performance are paramount.

9V block battery

Specifications: 9V batteries are rectangular, measuring approximately 26.5mm x 17.5mm x 48.5mm. They provide a 9V voltage and a capacity typically ranging from 400mAh to 600mAh.
Features: Devices requiring multiple cells or compact power sources commonly use 9V block batteries, which provide high voltage.
Suitability: This product is suitable for specific flashlight models, smoke detectors, wireless microphones, and other devices requiring a reliable and long-lasting power supply.

Other types of flashlight batteries:

6V block battery

Specifications: 6V block batteries typically have dimensions of approximately 34mm x 17mm x 67mm, providing a voltage of 6V and a capacity normally ranging from 4000mAh to 8000mAh.
Features: 6V block batteries offer higher voltage than standard AA or AAA batteries, making them suitable for specific flashlight models and devices requiring higher power output.
Suitability: It is commonly used in older flashlight designs, portable spotlights, and emergency lighting systems where compatibility with 6V power sources is essential.

12V block battery

Specifications: 12V block batteries have dimensions of approximately 34mm x 17mm x 67mm, provide a voltage of 12V, and typically have a capacity ranging from 3000mAh to 6000mAh.
Features: 12V block batteries provide even higher voltage than 6V batteries, making them suitable for specific flashlight models and devices requiring 12 volts of power.
Suitability: Used in specialized flashlights, vehicle-mounted lights, and other applications where higher voltage is necessary for optimal performance.

4LR44 (AG13) battery

Specifications: 4LR44 batteries are button cell batteries with a diameter of 11.6mm and a thickness of 5.4mm. They provide a voltage of 1.5V and a capacity typically ranging from 100mAh to 200mAh.
Features: Despite their small size, 4LR44 batteries offer sufficient voltage and capacity for specific flashlight applications.
Suitability: Occasionally used in compact flashlights, keychain lights, and electronic devices requiring a low-profile power source.

Match Battery Size to Your Flashlight Type

EDC Pocket Lights: 16340 or 14500 sizes (compact dimensions)
Tactical Flashlights: 18650 (balance of power/size)
Search & Rescue Lights: 26650 or dual 18650 (max runtime)
Headlamps: AAA or proprietary flat packs (lightweight)

Part 4. Choosing tips for flashlight batteries

Understand Your Flashlight’s Requirements: Before choosing a battery, it’s essential to understand your flashlight’s specifications, including its voltage, size, and power consumption.
Consider Battery Chemistry: Flashlight batteries use various chemistries, such as lithium-ion, nickel-metal hydride (NiMH), and alkaline.
Evaluate Voltage and Capacity: Pay attention to the battery’s voltage and capacity, as these factors directly impact the flashlight’s runtime and performance. Higher voltage batteries generally provide more power, while higher capacity batteries offer longer runtime between charges or replacements.
Check Size and Form Factor: Using a battery that is too large or too small may result in poor fitment or damage to the flashlight.
Consider Rechargeable Options: Rechargeable batteries can be a cost-effective and eco-friendly choice for frequent flashlight users. Consider investing in rechargeable lithium-ion or NiMH batteries and a compatible charger for long-term savings and convenience.
Check Compatibility: Some flashlights only work with specific battery types or brands, as their design dictates. Check the manufacturer’s recommendations to ensure compatibility and avoid damaging your flashlight.
Evaluate Environmental Conditions: Consider the environmental conditions in which you’ll use your flashlight. For extreme temperatures or outdoor activities, choose batteries with high-performance ratings and durability to withstand harsh conditions.
Consider Long-Term Costs: Rechargeable batteries may have a higher upfront cost, but they can save money in the long run compared to disposable batteries.

Part 5. FAQs about flashlight battery sizes

What are the standard flashlight battery sizes?

The 5 most common standard flashlight battery sizes are:

AA (14.5×50.5mm) – 60% of household flashlights
AAA (10.5×44.5mm) – Compact and headlamps
18650 (18x65mm) – Professional/tactical lights
CR123A (17x34mm) – Emergency and tactical
D Cell (34.2×61.5mm) – High-power lanterns

What is the difference between 18650 and 26650 batteries?

The 26650 (26mm diameter) is larger than the 18650 (18mm diameter), offering 30-40% more capacity (4000-5000mAh vs 2500-3500mAh). This makes 26650 ideal for extended outdoor use while 18650 balances power and compactness.

How to measure flashlight battery size?

Use this 3-step measurement method:

Measure diameter in millimeters (use digital calipers)
Measure length excluding terminals
Check battery markings (e.g. “18650” = 18mm diameter × 65mm length) Always measure your flashlight’s compartment for compatibility.

Can I use AA batteries instead of 14500?

No. Although they are the same size (14x50mm), AA batteries are 1.5V, while 14500 lithium batteries are 3.7V. Using 14500 in AA-only flashlights may damage electronics. Always check voltage requirements.

Which battery size lasts longest?

D Cell batteries provide the most extended runtime (5000-10000mAh), followed by 26650 lithium (4000-5000mAh). For everyday use, 18650 offers the best balance of runtime and portability.

Are larger battery sizes always better?

Not necessarily. While larger batteries (like 26650) offer more capacity, they add significant weight and size. Choose runtime (larger sizes) vs portability (18650/AA) based on your priority.

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