How Long Can a Car Charge a Phone Without Starting the Engine?
2 Answers
When a car is not started, it can charge a phone for about one hour. Precautions for charging a phone in a car without starting the engine: The car battery has a certain voltage. When the voltage drops below 13.4V, starting the car becomes difficult. Charging a battery at this voltage generally requires maintaining an engine speed above 1500 RPM, and sometimes even above 1700 RPM. If the battery doesn't have enough power to start the engine, keeping the engine speed above 1500 RPM for more than 20 minutes can provide enough charge for one start. Maintaining this speed for over 30 minutes can ensure enough power for starting the car the next day. Precautions for using a car battery: Avoid using electronic devices in the car for extended periods when the engine is off. Also, do not turn on power-intensive devices like headlights or the air conditioner simultaneously when starting the engine.
I often charge my phone in the car, relying on the battery when the engine is off. Generally, a standard car battery has a capacity of around 60 ampere-hours, while a phone battery is about 3000 milliampere-hours, and the charger draws approximately 1 ampere. Charging once doesn’t consume much power—theoretically, you could charge it over a dozen times. However, in practice, avoid discharging the car battery beyond 50% depth to prevent draining it. I’ve tested charging for up to 2-3 hours without issues starting the car, but prolonged charging carries risks, especially in older cars or cold weather. To maintain battery health, limit charging to 1-2 hours. Regularly check the battery voltage with a multimeter—stop charging if it drops below 12 volts. After all, car batteries aren’t designed for prolonged discharge, and replacing a damaged one is both troublesome and costly.
