Cylindrical cells (like the popular 32650 or newer 40135 sizes) look like oversized AA batteries. They are manufactured by rolling the anode, cathode, and separator tightly and encasing them in a rigid metal cylinder. The market primarily offers two shapes: Prismatic and Cylindrical. When designing or sourcing a LiFePO4 battery bank for solar energy storage, selecting the correct cell form factor. The type of battery cell (pouch, prismatic, or cylindrical) is the foundation of your battery's performance, reliability, and safety. Batteries with different material systems have different advantages. Among them, cylindrical batteries are mainly steel-cased cylindrical lithium iron phosphate batteries. 18650 => ~18mm in diameter and ~65.