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Fenix 21700U Rechargeable Li-ion Battery with USB Port


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SKU: FX-ARB-L21-5000U Categories: , , ,

The Fenix ARB-L21-5000U is a 21700 (21mm X 70mm) rechargeable Li-ion battery with integrated, direct-connect Type-C USB charging port (cord sold separately).  For comparison, a typical 18650 battery is 18mm X 65mm. This new size lithium ion is a replacement for flashlights that can accept the larger battery such as the Fenix PD36R and TK22UE.  With its 3.6 volts of power and 5000mAh capacity make it the perfect companion for high-drain flashlights, providing sufficient power and extra-long runtimes. Fitted with multiple protection systems, the button-top Fenix ARB-L21-5000U has 3 sets of overheat protection to ensure that the battery remains at a sustainable temperature. There are protection circuits embedded into the anode for overcharge, over-discharge, and short circuit protection as well. The steel shell riveting encasing the battery decreases any potential risk of the cell short-circuiting due to impacts, drops, or collisions combined with the pressure relief vents which will expel generated gas from a potential short-circuit to eliminate hazardous conditions within the battery


  • Fenix ARB-L21-21700U Rechargeable Button-Top 18650 Battery with integrated direct-connect Type-C USB Charging Port (USB cord sold separately) 
  • Equipped with multi-color LED - RED - charging; BLUE = charging completed
  • Lithium-ion; Button-Top Design
  • 3.6V 5000mAh
  • Max Charging Current: 1.0A recommended; 5A maximum
  • 7.5A maximum current
  • Protection circuit built-in the anode with a steel hat by riveting process. Steel shell eliminates the risk of short circuit caused by collision and impact.
  • Pressure Relief Vent: Expels waste gas generated by internal short circuit. Expelling waste gas prevents a cell from inflating or exploding.
  • Three Sets of Over-Heat Protection:  Over charge protection, Over discharge protection, Short circuit protection, and overheating protection
  • 500 Charge Cycles: Properly maintained, battery is designed to retain up to 75% of its original capacity at 500 full charge and discharge cycles
  • Weight: 2.56 Ounces
  • Height: 2.99"
  • Diameter: 0.85"
  • Note: You may also charge your 21700U in an external charger if your desire. Please consider, many older external chargers are sized to fit batteries to a maximum of 65mm in length.  21700 batteries are 70mm in length.  Be sure to double-check your existing flashlight and external charger specifications.


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