How many hours does it take to fully charge a dead car battery?

[MacLucille]

A dead car battery generally takes about 15 to 20 hours to fully charge. Precautions for battery charging include: 1. Connect directly to the battery for charging, avoiding removal of the battery to prevent data loss; 2. If the battery voltage is 10% lower than the rated voltage, it may lead to battery discharge; 3. Avoid water contact with the battery during charging. The functions of the battery are: 1. When starting the engine, the battery supplies power to the starting system, ignition system, and electronic fuel injection system; 2. When the engine is off or at low idle, it powers the vehicle's electrical equipment; 3. It can assist in powering electrical devices when the generator's output is insufficient; 4. It mitigates impact voltage in the electrical system, protecting the vehicle's electronic devices; 5. It stores excess electricity generated by the alternator.