Automotive emergency batteries are designed to start a vehicle's engine in case the main battery fails. There are specific starting current standards that these batteries must meet to ensure reliable engine starting.

　　The starting current required for an engine depends on several factors, including the engine size, type, and the ambient temperature. Generally, larger engines require a higher starting current. For a typical gasoline - powered car with a small to medium - sized engine (e.g., 1.0 - 2.0 liters), the starting current needed at normal ambient temperatures (around 20°C) is usually in the range of 200 - 600 amperes (A). However, as the temperature drops, the viscosity of the engine oil increases, and the engine becomes more difficult to start. At low temperatures, such as - 10°C, the starting current requirement can double or even triple.

　　Automotive emergency batteries are rated according to their cold - cranking amperes (CCA) and cranking amperes (CA). The CCA rating indicates the amount of current the battery can deliver at 0°F (- 18°C) for 30 seconds while maintaining a minimum voltage of 7.2 volts for a 12 - volt battery. This rating is crucial for ensuring that the battery can start the engine in cold - weather conditions. The CA rating, on the other hand, is measured at 32°F (0°C) and provides an indication of the battery's starting performance in milder cold conditions.

　　Manufacturers of automotive emergency batteries must design their products to meet or exceed these industry - standard ratings. A battery with a low CCA or CA rating may not be able to provide sufficient current to start the engine, especially in cold weather, leaving the vehicle immobilized. When choosing an automotive emergency battery, it's important to select one with a CCA and CA rating appropriate for the vehicle's engine size and the typical ambient temperatures in the area where the vehicle will be used.