How long does it take to fully charge a dead car battery by running the engine?

[NatalieLee]

If you want to charge a dead battery using the engine, take a 12V60Ah battery as an example. The charging method adopts constant voltage and current limiting: charge at 14.8V constant voltage and 15A current limiting for 16 hours, followed by 3A constant current charging for 4 hours, totaling 20 hours. The required charging time is relatively long. Here are some related details: 1. Other charging methods: If the battery is dead, it is recommended to use a battery charger to fully charge it. Typically, a household car battery has a capacity of around 60Ah, requiring a charging current of one-tenth of the battery capacity, which is 6A. Charging at this current usually takes about 3-5 hours to fully charge. 2. Battery lifespan: Car batteries are relatively consumable parts. With each charge and discharge cycle, the battery's performance deteriorates. Under normal circumstances, with proper usage habits, a battery can last 3-4 years, or even longer. 3. Battery maintenance: (1) If the car is not used for an extended period, it is advisable to disconnect the negative terminal of the battery. This prevents the battery from activating its self-protection function to discharge, avoiding a deep discharge state, which could lead to permanent battery failure. (2) Additionally, to minimize power consumption, it is recommended not to use high-power electronic devices such as headlights or audio systems for extended periods when the engine is not running.

[SanGiselle]

Last time I came back from a business trip, my car broke down. After getting a jump start from a friend, I drove on the ring highway for two hours straight. The mechanic said the key is how much the battery was drained—if it's completely dead, it takes four to five hours of driving with the alternator charging it. My Tiguan 1.8T took half an hour just to get the radio working again. Now I've made it a habit to use a charger for short commutes, especially in winter when the initial start-up consumes a lot of power. If the battery inspection hole turns black, it means it's time for a replacement. Last year, my Varta battery lasted five years before retiring.

[McNaomi]

Over the years in auto repair, I've encountered countless cases of dead batteries. The key factors are engine displacement and battery capacity. For a 2.0L vehicle with a 60Ah battery, the idle charging current is only 8 amps. Theoretically, it would take over ten hours to fully charge a depleted battery, but in reality, that's impossible—the alternator also has to power loads like the AC compressor and headlights. Once, a customer driving an Audi Q7 to pick up their kids couldn't start the car after just a 3-kilometer trip—the charge wasn't even enough to cover the starter's draw. They ended up replacing the battery. The most reliable solution is to jump-start the car and then drive on the highway for at least half an hour to stabilize the voltage at 14V.

[MacLuke]

Last time camping forgot to turn off the headlights. After jump-starting with emergency power, I deliberately monitored with a USB voltmeter. It took 15 minutes of city driving just to recover to 12.5V - full recharge requires sustained medium-high speed driving. Recommend buying a $10 battery monitor clip; if voltage drops below 12.2V the engine won't start. Start-stop batteries are even more delicate - incomplete charging reduces lifespan. Now I don't even dare charge my phone too long after turning off the engine, considering an AGM battery replacement costs over $2,000.