Yes, after the car battery is out of power, in theory, the use of portable charger to charge the battery takes 20 hours, if it is the engine ignition charge, it needs to be charged for more than 5 hours, and not in the case of idling, the speed is more than 2000 RPM.
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However, in fact, there is no need to worry about letting the car battery fully charged, as long as the car battery is enough to bring the engine to start the system fire, and as long as the engine has been in the ignition state, it will always charge the battery.
If it is not deep discharge (voltage below 10V), the car will charge itself when it is driven. If it has been overdischarged, the generator cannot be charged and must be repaired or replaced
The battery of this car will automatically charge as soon as the engine starts, so it does not need to be charged under normal circumstances.