An 18500 battery is a type of rechargeable Lithium Ion or LiFeP04 battery that is commonly used in electronic devices that require a high level of power output and extended run times, such as solar lights, flashlights, and other high-drain devices. The 18500 battery typically has a voltage of 3.7 volts and a capacity of between 1400 and 2000 mAh, which is higher than that of a standard AA battery. One of the key advantages of the 18500 battery is its rechargeability. It can be recharged multiple times, either in the electronic device or using a battery charger.