Li-ion cell vs battery pack

A lithium-ion cell (cylindrical, prismatic or pouch) has a nominal voltage set by its chemistry: around 3.6–3.7 V for common NMC and NCA types, about 3.2 V for LFP. Cells are wired in series to raise voltage ("4S" means four in series) and in parallel to raise capacity and current. For example, a 4S2P pack of 3.6 V cells has a nominal voltage of 14.4 V and twice the capacity of one cell.

A pack adds a protection circuit or full battery management system, interconnects (welded strips or busbars), temperature sensing, insulation, mechanical support and an enclosure. Pack design determines safety, cycle life and certification path far more than the choice of cell alone.

Where it bites: cells in series must be matched and balanced; a custom pack needs its own UN 38.3 and usually IEC 62133 testing; and changing cell supplier means re-qualification.