Fenix 21700 Rechargeable Battery h. The maximum current for the ARB-L21-4000P is 18A with a continuous output current of 10A. Why is this necessary? The higher current allows the 21700 battery longer runtimes in flashlights. As with all Fenix rechargeable batteries the 21700 4000mAH has three sets of overheat protection including pressure relief microporous and PTC cathodal block. Specifications for Fenix 4000mAh 21700 Rechargeable Battery: Manufacturer: Fenix Battery Quantity: 1 Battery Capacity: 4000 mAh Power: 3.6 volts Flashlight Model: Fenix PD40R V2.0 Fenix LR35R Fenix TK30 Fenix HT18 Fenix TK22 UE Fenix PD36R Diameter: 0.85 in Length: 2.99 in Weight: 2.5 oz Battery Type: 21700 Package Contents: Fenix 4000mAh 21700 Rechargeable Battery Fenix ARB-L21-4000P: 21700 Rechargeable Battery 4000mAh