Power various electronics, including all Fenix flashlights that use 16340 or CR123 batteries, with this ARB-L16-700UP 16340 Lithium-Ion Battery with Micro-USB Charging Port. You can just plug it in via the micro-USB, or use a separate charger (Fenix recommends its ARE-C1+, ARE-C2, ARE-C2+, ARE-X1+, or ARE-X2 chargers.) The battery features 3.6V of output power and a 700mAh capacity, and is equipped with a built-in protection circuit that safeguards against short-circuiting, overheating, and excessive charge/discharge current built into the anode. The three-way overheat protection design consists of a pressure relief valve, a microporous membrane separator, and a PTC cathode block. A steel shell adds durability. Expect up to 500 charge/discharge cycles, and the battery's low self-discharge rate allows it to maintain up to 75% of its capacity even beyond that. An LED status indicator light glows in red during charging and turns blue when the process is complete.