The batteries are made up of individual Li-ion cells designated 18650 because of their size (18mm x 65mm). These are very common batteries found in countless consumer electronics, electric bicycles, and even electric cars.
There are basically two types of 18650 cells- those made by the four major, name brand suppliers (Sony, LG, Panasonic, and Samsung), and everything else. The name brand cells are much safer and more reliable than the cheaper cells.
Pedego Electric Bikes use premium cells made by Samsung, which is the world’s largest Li-Ion battery supplier. SMART-e uses LG and Samsung batteries.