How Long Does It Take to Recharge a Dead Car Battery to Restart?

[Chloe]

It takes between 1 to 20 hours to recharge a dead car battery, depending on the remaining charge: 1. If the engine can start smoothly, the battery must have at least 50% charge left, requiring 1 to 2 hours for a full charge; 2. If idling, it will take 2 to 3 hours; 3. When the battery is severely depleted, a portable charger should be used immediately, requiring up to 20 hours for a full charge. A fully charged battery can be identified by the following signs, or by observing the charge indicator turning green: 1. A large number of bubbles appear in the battery, creating a 'boiling' effect; 2. The terminal voltage rises to its maximum and does not increase further within two hours; 3. The electrolyte level rises to its highest point and does not increase further within two hours.