Fenix 14500 battery is the AA size Li-Ion rechargeable battery that has two variations. The ARB-L14-800 battery is 3.6 Volt that is designed for the Fenix LD09, E25 Ultimate Edition, HL35, RC05 models in order to drive the light to new heights in their Turbo Mode. The ARB-L14-1600U built-in USB rechargeable battery is 1.5 Volt, designed to be a rechargeable alternative to a standard AA battery. However, the 1.5 Volt will not allow you to reach Turbo Mode in the models perfused before. This battery is quickly charged via micro-USB charging port, no need to carry a separate charger.
Note for the 1600U: Only charge using USB cable to USB port on battery. Do not charge by other device.