This Fenix rechargeable 21700 battery is designed for large current output. The maximum current for the ARB-L21-4000P is 18A, with a continuous output current of 10A. The higher current allows the 21700 battery longer runtimes at higher levels in flashlights. As with all Fenix rechargeable batteries, the 21700 4000 mAH has three sets of overheat protection, including pressure relief, microporous, and PTC cathodal block. The pressure relief vents all gas to be expelled; this prevents secondary hazards.