18650 batteries are a certain type of lithium-ion battery. They have this name because they are 18 mm by 65mm, which is then turned into the number 18650. They’re slightly bigger than AA batteries and are also the most common batteries used in vape devices. These 18650 cells have a 3.6 to 3.7 volt average rating during a complete discharge and have a complete range of 2.5 to 4.2 volts. These batteries are the most capable at getting you an awesome vape. Their capacity is measured in milliamps (mAh) and the maximum continuous discharge is in amperes (A). In the year 2015, the highest capacity 18650 batteries had around 3500mAh with the highest amperage of 30A. More than forty percent of all batteries are lithium-ion and 18650s make up the majority of those. These batteries are also quite safe to use; your safe if you use the right batteries.