The 18650 battery has been the most popular form factor when it comes to high-powered vaping. Named as such because these vape batteries are 18 mm wide and 65 mm high.
Though the size of a household AA battery, 18650 batteries are much more powerful. They're suitable for vape use will be rated at a minimum continuous discharge capability of 20 amp - anything less is unsafe to pair with the high power output that modern advanced vape hardware demand. The only manufacturers of batteries appropriate for vape use are LG, Sony, and Samsung, though several companies repackage or “rewrap” unidentified cells that may or may not be safe to use. So be careful.
Vape batteries, because they’re “unprotected” and capable of discharging a high amount of power require vapers to take special care to avoid dangerous situations.