How to Charge a Car Battery Using Another Battery?

[AddysonRose]

The steps to charge a car battery using another battery are as follows: 1. Prepare a charger that matches the voltage and capacity of the battery. Find the nearest car and move it close to the car with the dead battery, ensuring the front ends face each other. 2. Open the hoods of both cars, take out the charging clamps, and locate the batteries in both vehicles, which are clearly marked. 3. Identify the positive and negative terminals of the batteries—red is positive, and black is negative. Attach one end of the positive clamp to the dead car's positive terminal, then attach the other end to the positive terminal of the charged car's battery. 4. After all clamps are securely attached, start the charged car and charge for about five minutes. Then, try starting the dead car to see if it can turn on.

[SanRose]

Last time my car broke down and I called for roadside assistance, the technician taught me a standard procedure: park another car head-to-head with mine, connect positive to positive (red to red), and attach the negative clamp from the rescue vehicle to a metal frame on my car (avoid the battery negative). Start the rescue vehicle and rev the engine to 2000 RPM, wait five minutes, then try to start my car. After it starts, don’t rush to disconnect the cables—keep revving the engine for half an hour to charge the battery more steadily. The key is never to reverse the connection order. Cars nowadays are quite delicate, and a wrong connection could fry the ECU, which would be a huge loss. A friend of mine learned this the hard way.

[VanAdelyn]

Actually, keeping an emergency power supply is more convenient, something as compact as a power bank can jump-start your car. I always keep one in my car, and it's simple to use: clamp the red clip onto the battery's positive terminal (marked with a +), attach the black clip to any metal part of the engine, then press and hold the switch until the green light comes on to start the engine. The key is to operate it with the engine off. A special reminder for owners with auto start-stop systems: you'll need a dedicated model, as regular power supplies can't handle the sudden high current. Also, in cold weather, check the voltage frequently—if it drops below 11.8 volts, charge it immediately.

[McEzra]

Using a charger is the safest method. As an experienced driver, I recommend: Open the battery cover to expose the positive and negative terminals. Connect the red clamp to the positive terminal and the black clamp to the negative terminal, ensuring the clamps don't touch each other. After securing the connections, plug in the power and select the 12V mode, then set it to slow charging. A flashing green light on the charger indicates proper operation, and leaving it to charge overnight is more reliable. Remember to slightly open the car windows for ventilation during charging, and avoid doing this in an enclosed garage. If the battery is swollen or leaking, replace it immediately—forcing a charge is too dangerous.