The Fenix ARB-L21-5000U battery is a high quality, li-ion, 21700 with a capacity of 5000mAh. The battery has a built-in USB-C port which removes the requirement for a separate external charger.
The battery is compatible with Fenix 21700 powered torches.
To recharge simply plug a USB-C cable (not included) into the battery. The indicator will change from red to blue when fully charged, which takes approximately 4 hours.