If you own a Fenix RC10 or RC15, this power accessory will extend your flashlight runtime. It includes a ARB-L1 2600mAh 3.7 volt lithium-ion battery and a custom-fit charging receptacle. The unique foolproof reversible polarity design feature helps to make the battery easy to change in the dark. The battery has protection against overcharging, over-discharging and overheating. Keep a couple of these on hand your flashlight will always be ready to work.