How long can you charge your phone after the car is turned off?
4 Answers
Theoretically, you can charge your phone until it's fully charged after the car is turned off without any issues. This is because a phone battery typically has a capacity of just a few thousand milliampere-hours, while the car battery has a much larger capacity. However, it's best to avoid doing this for the following reasons: 1. High self-consumption: The power consumed by simply charging a phone is negligible, but the vehicle itself consumes a significant amount of power. 2. Battery drain: As long as the power is not cut off, all other electrical devices in the car remain powered on, which over time can easily lead to battery drain and even prevent the car from starting, as well as cause wear and tear on the battery. 3. Overload: After turning off the engine, try to avoid using any electrical devices in the car to prevent the battery from being overloaded, which can lead to battery drain.
I often charge my phone in the car while waiting with the engine off, and this duration mainly depends on the battery capacity. For a regular sedan, the 12V battery capacity ranges between 45Ah and 70Ah when the engine is off. Assuming a phone charging power of 10W, it could theoretically last five to six hours. However, in reality, you must account for the car's own power consumption, such as the alarm system and central locking, which also draw electricity. If the battery is already two or three years old, it might lose a third of its charge in just half an hour. Once, I had difficulty starting the car after charging for less than two hours, so I recommend not charging your phone for more than two hours, especially in older cars, or you might end up stranded. It’s best to charge while driving, as the charging efficiency is highest when the engine is running.
Last time camping, I tried using the car as a power bank while the engine was off. Found that how long it lasts depends on two things: first, the battery size - an SUV's high-capacity battery lasts much longer than a micro car's. Second, the phone's charging state - it consumes less power when idle with screen off, but drains faster while charging and gaming simultaneously. From my experience, a healthy fully-charged car battery can typically sustain charging a modern smartphone for about two hours. Beyond this, battery voltage drops noticeably, potentially affecting the ignition system. Especially in winter when battery performance declines - once at sub-zero temperatures, it triggered a warning after just half hour of charging. Remember to drive for at least twenty minutes after starting the vehicle before turning it off again, allowing the alternator to recharge the battery.
The battery becomes isolated after the engine is turned off. A standard car battery is approximately 48Ah, while the charging current for a mobile phone typically ranges from 0.5A to 2A. In theory, a fully charged battery can supply power for 24 to 96 hours, but this is only an ideal scenario. In reality, the vehicle's anti-theft system consumes about 0.02Ah per hour, and situations like leaving the headlights on can make things worse. In most cases, the safe duration is around one hour, after which the battery voltage may drop below 11V, potentially making it impossible to start the engine. It is advisable to develop the habit of checking the voltage before charging, and extra caution should be taken with older vehicles.
