How long does it take to charge a 12V battery to start the engine?
2 Answers
Generally, charging for more than 30 minutes with a 12A current can be tried to see if the engine can start. However, the time required to fully charge the battery depends on its size. For a 60AH battery, charging with a 12A current for about 5 hours can reach approximately 90% capacity. When the battery power is below half, i.e., the voltage is below 13.4V, the battery warning light will illuminate, and the car will be difficult to start. It is generally recommended to keep the battery above 20% charge. The chemical conversion efficiency during battery charging is about 50%, so charging requires adding 150%*80% of the power. Below is some related information: Electrolyte evaporation: The electrolyte (dilute sulfuric acid) inside the battery gradually evaporates as the battery temperature rises, especially during summer. Unscrewing the four sealing plugs on the battery will reveal anti-splash vent holes designed to release the steam generated inside the battery due to temperature increases. Function of the battery: To provide a large instantaneous current when starting the car, typically reaching dozens of amps or even more. After the engine is running normally, the battery's main role is to continuously supply power to the ignition coil, audio system, and other electrical devices. Simultaneously, the electricity generated by the alternator replenishes the battery, ensuring it does not run out of power during use.
I remember one time my car battery was dead, and a neighbor lent me a 12V charger to help charge it. The exact charging time depends on the situation: batteries come in different sizes. For a small car battery like a 40Ah one, if it's just slightly discharged, charging for 3-4 hours might be enough to start the engine. For a larger battery, say 60Ah or above, if it's deeply discharged, it might need 6-12 hours or even longer. I prefer using a smart charger, which automatically stops charging to avoid overcharging and damaging the battery. Don’t rush the charging process; it’s best to wait until the voltage reaches above 12.8V before attempting to start the car. Regular battery maintenance is also important to extend its lifespan. I recommend charging it overnight, and by morning, it should usually start without any issues.
