How long does it take to charge a dead car battery to start the engine?
4 Answers
Charging time for a dead car battery: Taking a 12V60Ah battery as an example, the charging method adopts constant voltage with current limiting. Charge at 14.8V constant voltage and 15A current limiting for 16 hours, then switch to 3A constant current charging for 4 hours, totaling 20 hours. A fully charged battery can be identified by the following phenomena, or by observing the charge indicator turning green. Below are the indicators of a fully charged battery: 1. A large number of bubbles are generated inside the battery, showing a "boiling" phenomenon. 2. The terminal voltage rises to the maximum value and does not increase further within two hours. 3. The electrolyte level rises to the highest position and does not increase further within two hours.
There's no fixed time for charging a dead car battery—it depends on the situation. From my experience with many vehicles, the charging speed is mainly determined by the current. With a standard charger (typically 5-10 amps), a fully depleted battery usually takes 4-8 hours to regain enough power for ignition. Fast chargers with higher currents may enable a start attempt in as little as 30 minutes, but I don't recommend frequent use as it accelerates battery aging. Temperature also plays a role—charging takes longer in cold weather. Always monitor the voltage; wait until it reaches at least 12.4V before attempting ignition to avoid failure. During charging, ensure secure and safe connections—attach the positive terminal first, then the negative. As a preventive measure, start your car weekly for 20 minutes to let the battery self-charge, reducing depletion risks and minimizing charging hassles.
I'm quite knowledgeable about charging times, which mainly depend on the charger's current and the battery's capacity. For example, with my small car, I usually use a 10-amp charger for a 55-amp-hour battery. When the battery is completely dead, it takes about 6 hours to charge it sufficiently for a reliable start. If I increase the current to 20 amps, it might only take an hour to attempt starting, but I always caution against frequent fast charging as it can damage the battery internally. The degree of discharge also matters—light discharge might only require 2 hours, while deep discharge could take overnight. I always remind everyone to check the charger's labeled current and calculate the time based on the battery's specifications. After starting, it's advisable to drive for half an hour to allow the battery to recharge, which is safer. Avoid operating in damp environments to prevent short circuits—safety should always come first.
Last time my car battery was completely drained, I tried using a household charger. Starting from zero charge, I trickle-charged it at 5 amps for about 5 hours until the voltage reached 12 volts, and it started right up. The time required varies depending on the charger's performance. Shallow discharges might charge faster, but a full recharge requires patience. While charging, I checked that all cable connections were tight, and before starting, I made sure there were no strange smells or overheating. After charging, I usually drive for a while to let the alternator recharge it. Remember, avoid fast charging to prolong battery life. I make it a habit to clean the battery terminals monthly to prevent corrosion, which can cause repeated drain—small maintenance can prevent big headaches.
