Fenix ARB-L18-3500: The Fenix ARB-L18-3500U USB rechargeable lithium-ion battery can be charged by its built-in USB port or by an external battery charger. A protective circuit is built into the anode and covered with a riveted steel hat. The battery is fully covered with the steel shell. The Micro USB charging port lets you charge the battery directly, button-top design and a pressure Relief Vent: Expels waste gas generated by internal short circuit. *Note- Does NOT include USB charging cable.