The Fenix ARB-L18-3400U USB rechargeable lithium-ion battery features a built-in USB port to charge without the need for an external charger, though one can be used if desired. Its anode circuit is specially encased in a steel housing, reducing the risk of short-circuiting from impact or collision due to the fully wrapped steel construction.
Note: This item is packaged and priced as one unit - one battery.