Battery Pack Technology and Health Assessment

An EV battery pack contains hundreds to thousands of individual lithium-ion cells arranged in series and parallel configurations. Tesla Model 3 uses 2170 cylindrical cells (4,416 cells in the long-range pack), while the Chevrolet Bolt uses pouch cells arranged in modules. Cells connected in series increase voltage—96 cells in series at 3.7V nominal each produce a 355V pack. Cells in parallel increase capacity—multiple cells in parallel form a cell group that increases ampere-hour capacity. The battery management system (BMS) monitors every cell group's voltage, temperature, and state of charge, balancing cells to prevent overcharge or deep discharge.