Description
Get flagship-level endurance without the flagship price with the genuine Fenix ARB-L21-4900, a protected 21700 button top battery that delivers an impressive 4900mAh capacity. Designed for high-output LED flashlights, headlamps, and outdoor lighting, it provides near-identical runtime to 5000mAh cells at a more accessible value. The integrated overcharge, over-discharge, and short-circuit protection ensures safe, worry-free operation, while the raised button top guarantees reliable contact in Fenix and most other 21700 flashlight brands. With excellent cycle life and Fenix's trusted quality, the ARB-L21-4900 is the smart choice for users who want maximum practical runtime without overpaying.
Key Features
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4900mAh Near-Flagship Capacity – Delivers virtually the same runtime as 5000mAh cells—only about 2% less. Provides approximately 40% more energy than a standard 3500mAh 18650. Ideal for users who want top-tier endurance at a better value.
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10A Continuous Discharge – Supplies stable, reliable power for demanding LED flashlights and outdoor equipment. Enough current for turbo modes and high-output settings without triggering protection.
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Built-in Protection Circuit – Safeguards against overcharge (4.2V cutoff), over-discharge (2.5V cutoff), short circuits, and overcurrent (10A limit), protecting both the battery and your valuable devices.
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Button Top Design – Raised positive terminal ensures reliable electrical contact in Fenix and most other 21700 flashlights and devices requiring a button top.
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Long Cycle Life – Retains over 80% of initial capacity after 500 charge/discharge cycles under recommended conditions, reducing long-term replacement costs.
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Fenix Genuine Quality – Manufactured to strict standards with a premium 21700 cell core and advanced protection circuitry for consistent, safe performance.
Parameters
Applications
Recommended For
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High-Output 21700 LED Flashlights: Perfect for Fenix and other 21700-powered flashlights. The 4900mAh capacity provides near-flagship runtime—approximately 40% more energy than a standard 3500mAh 18650 cell. Ideal for everyday carry, professional use, and extended outdoor adventures.
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Headlamps for Outdoor & Professional Use: Extended runtime for camping, running, caving, and industrial applications. The protection circuit prevents over-discharge damage when lights are accidentally left on.
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Camping Lanterns & Emergency Lights: Reliable power for extended trips and power outages. The 4900mAh capacity ensures lights stay on through the longest nights.
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Bicycle Lights: Consistent output for night riding, endurance events, and multi-day touring without battery changes.
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Smart Doorbells & Wireless Security Cameras (21700 Compatible): Ultra-long standby with reliable power for motion detection and recording events.
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Portable Fans & Outdoor Gadgets: Suitable for any 21700-powered device drawing under 10A where long runtime is desired.
Not Recommended For
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High-Power Vaping / Mechanical Mods: These require 15–35A unprotected cells. The 10A protection limit is insufficient for sub-ohm applications.
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Cordless Power Tools: Drills, saws, and impact drivers demand 20–40A continuous current, far beyond this battery's 10A protection limit.
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RC Cars, Drones & High-Drain Models: These require 20–30A+ continuous current. This battery will not function and may trigger protection.
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18650-Only Devices: This is a 21700 cell (21mm diameter) and will not physically fit in 18650 battery compartments.
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Multi-Cell Series Packs: Individual protection boards may conflict. Use matched unprotected cells with an external BMS instead.
FAQ
Q: How does the 4900mAh compare to 5000mAh cells? Is the difference noticeable?
A: The ARB-L21-4900 provides 4900mAh, which is only about 2% less capacity than a 5000mAh cell. In real-world use, the difference is negligible—perhaps 5–10 minutes less runtime on high mode in a typical flashlight. For the vast majority of users, the practical runtime is essentially identical, often at a more attractive price point.
Q: Is this battery compatible with my Fenix 21700 flashlight?
A: Yes. The ARB-L21-4900 is specifically designed for Fenix 21700 flashlights and is compatible with most other brands requiring a button top 21700 cell. Due to the protection circuit and button top, the battery is approximately 71mm long. Most 21700 flashlights are designed to accommodate protected cells, but please verify your device's battery compartment length before ordering.
Q: Can I use this battery in my 18650 device?
A: No. The 21700 format has a larger diameter (21mm vs. 18mm for 18650) and will not physically fit into 18650 battery compartments. Only use this battery in devices specifically designed for 21700 cells.
Q: What does "protected" mean and why should I choose a protected cell?
A: A protected cell has a built-in circuit board that automatically prevents overcharge (above 4.2V), over-discharge (below 2.5V), short circuits, and excessive current draw (above 10A). This makes single-cell use significantly safer, especially in devices without their own battery management. The trade-off is a slightly longer cell (~71mm vs. ~70mm) and a current limit of 10A.
Q: Can I use this battery for vaping or power tools?
A: No. Vaping devices and power tools require high continuous currents (typically 15–40A). The ARB-L21-4900's protection circuit limits output to approximately 10A. Using it in such devices will cause the protection to cut off power or may damage the battery. Please use dedicated unprotected high-drain cells for those applications.
Q: How should I charge and store this battery?
A: Use a quality lithium-ion battery charger with a CC-CV algorithm designed for 21700 cells. Fenix chargers are an excellent match. Charge at 0.5C (2.45A) for best longevity. Store at approximately 3.6–3.7V (40–50% charge) in a cool, dry place using a non-conductive battery case. Avoid storing fully charged or fully discharged for extended periods.
