This paper compares CO₂ emissions, energy use, operating costs, and external climate costs of light commercial vehicles (N1-I–N1-III) with spark-ignition, compression-ignition, and battery-electric propulsion, operating under the Polish electricity mix. Fuel and electricity consumption, as well as CO₂ emissions, for ICE vehicles were obtained from the COPERT 5 model, while BEV emissions were calculated using national KOBiZE emission factors. Annual mileage was set at 30,000 km. The results show that BEVs reduce CO₂ emissions by approximately 25–50% and energy costs by 35–55% compared with combustion vehicles, with the most significant benefits in the heaviest N1-III class. External costs of CO₂ are also substantially lower for BEVs. However, the high carbon intensity of the Polish power sector limits achievable reductions, underscoring that fleet electrification must be accompanied by power system decarbonization to fully exploit its climate benefits.