Quick Answer

Choose a Fenix rechargeable battery that matches your device's required size and capacity. The ARB-L21-5000 V2.0 is a high-capacity 21700 cell for powerful flashlights, while the ARB-L16-700U is a smaller 16340 battery with a built-in USB plug for convenience. Always check your light's specifications before buying.

Understanding Battery Sizes and Compatibility

Fenix rechargeable batteries come in different physical sizes—like 21700, 18650, and 16340—that correspond to the battery tube of your flashlight or headlamp. Using the wrong size can damage the device or prevent it from powering on. Always consult your light's manual or product page to confirm which battery format it accepts before purchasing a replacement or spare.

Capacity vs. Convenience

Higher capacity (mAh) means longer runtime between charges, but it often comes with a larger physical size. The ARB-L21-5000 V2.0 offers up to 5000mAh in a 21700 format, ideal for extended use in high-drain lights. In contrast, the ARB-L16-700U has a lower 700mAh capacity but fits smaller devices and includes a built-in micro-USB port for charging without a separate charger. Your choice depends on whether you prioritize runtime or portability.

Frequently Asked Questions About Fenix Rechargeable Batteries

Can I use any rechargeable battery in my Fenix light?

No. Fenix lights are designed for specific battery sizes and chemistries. Using an incompatible battery can cause poor performance or damage. Always match the battery type (e.g., 21700, 18650, 16340) listed in your light's specifications. Check your device manual before buying a replacement battery.

What is the advantage of a built-in USB charging port on a battery?

A battery like the ARB-L16-700U with a built-in micro-USB port lets you recharge it directly from any USB source—no separate charger needed. This reduces gear weight and simplifies charging when traveling. Great for minimalist kits or when you don't want to carry a dedicated charger.

How do I know if a battery has safety protections?

Look for features like a protection circuit in the anode (to prevent short circuits, over charge/discharge, and overheating) and pressure relief vents. The ARB-L21-5000 V2.0 includes both, providing an extra layer of safety. Protected batteries are recommended for reliable and safe operation.

  • Fenix ARB-L21-5000 V2.0 Rechargeable Battery: The ARB-L21-5000 V2.0 is a high-capacity 21700 Li-ion rechargeable battery built for more power and longer runtimes. It includes a protection circuit in the anode to help prevent short circuits, over charge/discharge and over heating, plus pressure relief vents that expel waste gas in the rare case of an internal short circuit. This battery is a strong choice for Fenix flashlights that accept 21700 cells, giving you maximum runtime and built-in safety features for peace of mind during long outdoor trips.
  • Fenix ARB-L16-700U Built-in USB Rechargeable Battery- DSICONTINUED: The ARB-L16-700U includes a protection circuit in the anode to help prevent short circuits, over charge/discharge and over heating. It can be charged quickly without a separate charger by plugging a micro-USB cable directly into the battery. If you own a smaller Fenix light that uses 16340 batteries, this model saves you from carrying an extra charger—just plug in a USB cable wherever you are.