On the final‑assembly line of a passenger‑car plant, the battery is installed directly into the vehicle’s chassis to supply the starter motor and all on‑board electronics during the functional‑test phase. As the body moves through the line, the battery provides the energy needed for the engine‑start sequence, power‑window operation, lighting, and infotainment checks, allowing technicians to verify that every control unit communicates correctly before the car leaves the factory. In electric‑vehicle production, the same battery unit powers the high‑voltage test rig that simulates driving conditions, enabling the validation of motor performance and energy‑management software without using the vehicle’s own propulsion cells. Because the battery is a self‑contained source, it can be swapped quickly between test stations, keeping the line moving and reducing downtime. The same component is later stocked for after‑sales service, where it is fitted as a replacement in warranty repairs or in routine maintenance, ensuring that the vehicle returns to the road with reliable start‑up capability. This dual role streamlines both production testing and field service.