Slightly larger than the AA battery, an 18650 battery (classified by its 18mm x 65mm size) is a rechargeable lithium-ion battery often used in battery packs, energy storage devices, drones, electric vehicles and other high-drain devices. Before using 18650 batteries, check with your device manufacturer for compatibility. With more than 100 available 18650 products at IMRbatteries.com, browse our most popular 18650 battery brands including: Samsung, LG and Sony Murata.