Description
Maximize your runtime to the absolute limit with the genuine Fenix ARB-L21-5800, the highest-capacity 21700 battery in Fenix's lineup. Built around an ultra-high-capacity 5800mAh cell core, this protected button top battery delivers approximately 16% more runtime than standard 5000mAh 21700 cells—making it the ultimate power solution for extended missions, multi-day adventures, and professional applications where changing batteries is inconvenient or impossible. 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. For users who refuse to compromise on runtime, the ARB-L21-5800 is the undisputed endurance champion.
Key Features
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5800mAh Maximum 21700 Capacity – The highest capacity battery in the Fenix 21700 lineup. Provides approximately 16% more runtime than 5000mAh cells and about 65% more energy than a standard 3500mAh 18650.
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10A Continuous Discharge – Delivers 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), ensuring safe operation and protecting 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 in demanding applications.
Parameters
Applications
Recommended For
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High-Output 21700 LED Flashlights: Perfect for Fenix and other 21700-powered flashlights. The 5800mAh capacity delivers the longest illumination time available in a protected 21700 cell—ideal for search and rescue, professional inspection, and extended outdoor expeditions.
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Headlamps for Professional & Outdoor Use: Designed for cave exploration, long-distance trail running, industrial inspection, and multi-day camping. The protection circuit prevents over-discharge damage during extended use.
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Camping Lanterns & Emergency Lights: Reliable power for extended power outages and off-grid living. The 5800mAh capacity ensures lights stay on through the longest nights.
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Bicycle Lights for Ultra-Endurance: Perfect for 24-hour races, multi-day bikepacking, and long-distance touring. Single-cell runtime covers entire events without battery changes.
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Smart Doorbells & Wireless Security Cameras (21700 Compatible): Months of standby time with reliable power for motion detection and recording events.
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Search & Rescue Equipment: When missions extend beyond expected timeframes, the extra 800mAh over standard 5000mAh cells provides a critical safety margin.
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Portable Fans & Outdoor Gadgets: Suitable for any 21700-powered device drawing under 10A where maximum runtime is the priority.
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: Is 5800mAh the real capacity? How much more runtime does it give compared to 5000mAh?
A: Yes. The ARB-L21-5800 uses an ultra-high-capacity 21700 cell core that delivers a true 5800mAh under standard test conditions. Compared to a 5000mAh 21700 cell, this provides approximately 16% more runtime. In a typical flashlight on high mode, this could mean an extra 30–45 minutes of illumination. Compared to a 3500mAh 18650, it offers about 65% more energy.
Q: Is this battery compatible with my Fenix 21700 flashlight?
A: Yes. The ARB-L21-5800 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 71.5mm 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 does it matter?
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 (71.5mm 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-L21-5800'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 (2.9A) 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.
