Fenix ARB-L21-5000 V2 Rechargeable 21700 Rechargeable BatteryFenix ARB L21 5000 V2 rechargeable 21700 battery provides the voltage and power needed for extended runtime and higher lumen capacities. The ARB L21 comes with all the bells and whistles of high quality Fenix batteries, including protective circuits inside the anode and up to 500 charging cycles. Also included are the three sets of overheat protection: pressure relief, microporous, and PTC cathodal block. Don't run out of light; pick up a spare 21700