Will turning on the air conditioning while starting the engine drain the battery?

[Mandy]

Turning on the air conditioning while starting the engine will not drain the battery. The battery's response before and after the car starts: 1. When the car is not started. The compressor does not work and cannot cool, only the fan is running. At this time, the car battery can support it for a long time. This is also to prevent damage to the battery when the compressor is working. Do not turn on the air conditioning when the engine is not started, because before the generator starts, the car's electrical appliances are powered by the battery. 2. After the car starts. The electrical energy is provided by the car's generator, and the air conditioning compressor will work and start cooling. At this time, the generator will also charge the battery. After starting, the battery is only charged and not used, as all power is supplied by the generator, so it does not consume the battery's power.

[CarsonDella]

I've been driving for many years, and I often see people worrying that turning on the air conditioning after ignition might drain the battery. Actually, it depends on the situation. If you normally start the engine and then turn on the AC, there's no problem at all, because while the engine is running, the alternator charges the battery while also powering the AC system, so the battery won't easily run out. I made a mistake when I was younger—once while waiting for someone in a parking lot, I turned the key to the ACC position without starting the engine and then turned on the AC and music. Half an hour later, the car almost wouldn't start. So the correct approach is to ensure the engine is running before using high-power electrical devices like the AC or heater; otherwise, relying solely on the battery will drain it quickly. Additionally, if the battery is aging or in cold winter temperatures, its discharge capacity decreases, making problems more likely. I recommend checking the battery status monthly, and if you notice slow starts, replace it early.

[DiElla]

From a technical perspective, whether turning on the AC while ignition depletes the battery depends on the engine status. Under normal circumstances, once the engine is running, the alternator starts working, supplying power to the entire vehicle system including the AC, while simultaneously recharging the battery. Thus, the battery charge won't decrease. However, if the engine isn't started and only the ignition is in the ACC or ON position, the AC compressor is powered directly by the battery, which can consume several hundred watts. This can quickly drain the battery, especially older ones. I've tested that running the AC in cooling mode without starting the engine can drop the battery voltage to a critical level in about 20 minutes. Therefore, it's advisable to develop the habit of turning on the AC only after starting the vehicle to avoid prolonged standby power consumption.

[Cory]

As an ordinary driver, I understand the concern about turning on the air conditioning while starting the car consuming electricity, but this depends more on the operation. In reality, it is safe to use the air conditioning after the engine is started and will not cause a power shortage. However, turning on the air conditioning while only igniting the car without starting the engine does consume electricity, similar to listening to the radio or charging a phone without running the engine, which can drain the battery. It is recommended to adjust the air conditioning settings after each start and regularly check the battery health, especially during extreme hot or cold seasons.