How to Charge a Car Battery

There are many reasons why a car battery might die, such as leaving the car idle for an extended period, exposing the battery to freezing temperatures, or leaving the lights on overnight with the engine off. To recharge a dead battery, you will need a jump starter cable and a functioning vehicle. Then, you connect the two batteries with the jumper cables, allowing power to transfer from the working car to charge the dead one. Continue reading below for a step-by-step guide on how to safely and effectively recharge a dead battery.

Inspect the external condition of the battery before charging. The battery should be intact, with no cracks or signs of acid leakage.

• Do not attempt to charge the battery if it shows signs of damage, as this could lead to injury for you or others.

Wear safety goggles and rubber gloves before handling a dead car battery. Goggles and gloves help protect your eyes and hands from acid splashes from the battery.

Position the jump-start car next to the vehicle with the dead battery, but make sure the two cars don’t touch. The ideal setup for charging a dead battery is to place both cars close together, facing the same direction, or place them head-to-head.

• Check that the distance between the two batteries is short enough for the jumper cables to reach. Jumper cable lengths vary depending on the type and manufacturer.
• Do not attempt to connect mismatched cables if the first set is not long enough. This could cause the cables to overheat and catch fire.

Take note of the positive and negative terminals on each battery. The positive terminal will be marked with a plus sign (+), and the negative terminal will be marked with a minus sign (-).

Connect the positive jumper cable to the positive terminals of both batteries. The positive jumper cable is typically red unless otherwise marked. The order in which you connect the jumper cables matters, so follow this sequence: First, attach one end of the positive cable to the dead battery, then connect the other end to the positive terminal of the working battery.

Attach one end of the negative jumper cable to the negative terminal of the working battery. Typically, the negative jumper cable is black.

Connect the other end of the negative cable to a metal, grounded part of the vehicle with the dead battery. This step grounds the car with the dead battery when it starts. You can attach the cable to the car’s frame, body, or another clean, rust-free part that is not painted.

Start the jump-start car. When the engine is running, the vehicle's charging system will begin transferring power to the dead battery through the jumper cables.

Wait at least five minutes after starting the jump-start car. This waiting period allows the dead battery to accumulate some charge, although more time may be needed to fully recharge it.

Start the car with the dead battery. If the battery has charged sufficiently, the engine should start with ease.

• If the engine still doesn't start, wait an additional five minutes to allow more charge to accumulate in the dead battery.

Once the engine is running, disconnect the jumper cables in the reverse order of connection. This will prevent any electrical surges or sparks from causing damage or danger.

• First, remove the ground cable, then the negative cable from the dead battery, followed by the positive cable from the jump-start car, and finally, the positive cable from the recharged battery.

Keep the car that is charging the battery running for at least another five minutes. This helps the alternator continue to recharge the battery further.

Run the vehicle for at least 20 minutes (either by driving or idling). In some cases, the battery will be fully charged during this time. However, you may need to replace the battery if the old one cannot hold enough charge to start the car.