Fenix ARB-L18-4000 18650 4000mAh 5A 3.6V Button Top Protected Battery – Ultra High Capacity for Flashlights & Headlamps

Description

Push your runtime to the absolute limit with the genuine Fenix ARB-L18-4000, the highest-capacity 18650 battery in Fenix's lineup. Built around the premium Panasonic NCR18650G 4000mAh cell core, this protected button top battery delivers an unmatched 4000mAh of energy—approximately 14% more runtime than standard 3500mAh cells. Integrated overcharge, over-discharge, and short-circuit protection ensure safe operation, while the raised button top guarantees reliable contact in Fenix, Streamlight, and most other major flashlight brands. For users who demand the longest possible runtime from a single 18650 cell, the ARB-L18-4000 is the ultimate power solution.

Key Features

• 4000mAh Maximum 18650 Capacity – Powered by the genuine Panasonic NCR18650G cell core, delivering the highest capacity available in a mass-produced 18650 battery. Ideal for users who need the longest possible runtime between charges.

• Built-in Protection Circuit – Safeguards against overcharge (4.2V cutoff), over-discharge (2.5V cutoff), short circuits, and overcurrent, protecting both the battery and your valuable devices.

• Button Top Design – Raised positive terminal ensures reliable electrical contact in Fenix, Streamlight, and most other 18650 flashlights and devices requiring a button top.

• Long Cycle Life – Retains over 80% of its initial capacity after 500 charge/discharge cycles, reducing long-term replacement costs.

• Fenix Genuine Quality – Manufactured to strict standards with an authentic Panasonic cell core and premium protection circuitry for consistent, safe performance in demanding applications.

• Wide Compatibility – Ideal for single-cell LED torches, headlamps, camping lanterns, bicycle lights, and other outdoor illumination equipment drawing under 5A.

Parameters

Applications

Recommended For

• LED Flashlights & Tactical Torches: Perfect for Fenix, Streamlight, and other quality brands requiring a button top 18650. The 4000mAh capacity delivers the longest possible illumination time from a single 18650 cell—ideal for extended trips, search and rescue, or professional use where changing batteries is inconvenient.

• Headlamps for Outdoor & Professional Use: Ideal for camping, running, caving, and industrial work. The protection circuit prevents over-discharge damage when lights are accidentally left on, and the massive capacity reduces the need to carry spare batteries.

• Camping Lanterns & Emergency Lights: Reliable power for extended trips and power outages. The 4000mAh capacity ensures lights stay on through the longest nights.

• Bicycle Lights: Consistent output for night riding. Single-cell runtime easily covers multi-day touring or ultra-endurance events without battery changes.

• Smart Doorbells & Wireless Security Cameras: Many video doorbells use 18650 cells. The ARB-L18-4000 provides the longest possible runtime between charges.

• Portable Fans & Outdoor Gadgets: Suitable for any 18650-powered device drawing under 5A where maximum runtime is desired.

Not Recommended For

• High-Power Vaping / Mechanical Mods: These require 15–35A unprotected cells. The protection circuit will cut off power under heavy loads.

• Cordless Power Tools: Drills, saws, and impact drivers demand 15–40A, far beyond this battery's 5A limit.

• RC Cars, Drones & High-Drain RC Models: These require 10–30A+ continuous current. This battery will not function and may trigger protection.

• Ultra-Compact Flashlights with Tight 65mm Battery Tubes: The protected button top design adds length (~68.5mm). Some compact lights may not close fully. Always verify your device can accommodate the extra length.

• Multi-Cell Series Packs: Individual protection boards may conflict. Use matched unprotected cells with an external BMS instead.

FAQ

Q: Is 4000mAh the real capacity? How does it compare to 3500mAh cells?
A: Yes. The Fenix ARB-L18-4000 uses the Panasonic NCR18650G cell core, which is currently the highest-capacity mass-produced 18650 cell available. Under standard test conditions, it delivers a true 4000mAh. Compared to 3500mAh cells, this provides approximately 14% more runtime—meaning an extra 30-40 minutes on high mode or several additional hours on low mode in a typical flashlight.

Q: Is this battery compatible with my Streamlight / Fenix / other brand flashlight?
A: If your flashlight accepts 18650 batteries and requires a button top (raised positive terminal), then yes. The ARB-L18-4000 is compatible with most Fenix and Streamlight models, as well as many other major flashlight brands. Due to the protection circuit and button top, the battery is approximately 68.5mm long. Some ultra-compact lights with very tight battery tubes may not close properly. Please check your device's battery compartment length before ordering.

Q: What does "protected" mean and why should I choose a protected cell?
A: A protected cell has a small circuit board added to the negative end that automatically prevents overcharge (above 4.2V), over-discharge (below 2.5V), short circuits, and excessive current draw. This makes single-cell use much safer, especially in devices without their own battery management. The trade-off is a slightly longer cell (68.5mm vs. 65mm) and a current limit of around 5A.

Q: Can I use this battery for vaping, RC cars, or power tools?
A: No. These applications require high continuous currents (typically 15–35A or more). The ARB-L18-4000's protection circuit limits current to approximately 5A. 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 this battery?
A: Use a quality lithium-ion battery charger with a CC-CV algorithm designed for 18650 cells. Fenix chargers are an excellent match. Charge at 0.5C (2.0A) for best longevity. The built-in protection circuit provides an additional safety layer, but a good charger is still essential. Never use damaged or low-quality chargers.

Q: How should I store this battery when not in use?
A: Store at approximately 3.6–3.7V (40–50% charge) in a cool, dry place. Use a non-conductive battery case to prevent accidental short circuits. Avoid storing fully charged or fully discharged for extended periods, as this accelerates capacity loss.