How to Charge a Car Battery

A number of things can drain a car battery enough to prevent the engine from starting. Someone left the lights on. Corrosion on the terminals is preventing a good charge. And the most annoying and sneaky – the dome light was left on all night. Regardless who or what is to blame, here’s how to charge a car battery so you can get back to driving.

Step-by-step: How to charge a car battery using a battery charger

You can get a decent car battery charger at just about any auto parts store or home center for about $50. Top-shelf models with more features can push $100. They’re nice to keep around the garage for emergencies. One use is enough to justify the cost.

First, ensure the battery charger is turned off before beginning. I like to unplug it just to be sure.

Next, pop the hood and locate the battery. On some newer vehicles, it’s located under the rear seat or in some other equally annoying place. In these cases, locate the positive terminal under the hood the automaker provides for just these cases. It’s often under a plastic cap that must be flipped open.

Now’s the perfect time to look for battery-terminal corrosion. White, flaky residue can build up on the terminals and interfere with a good connection, preventing the alternator from charging the battery (which may explain your current predicament). If that’s the case, clean the terminals first, which we show you how to do in this post. (By the way, AMSOIL Heavy-Duty Metal Protector does a great job helping prevent terminal corrosion.)

Connect the positive (red) clamp on the charger to the positive (red) car battery terminal.

If the battery is accessible under the hood, connect the negative (black) clamp on the charger to the negative (black) car battery terminal.

If the battery is buried under the back seat or elsewhere, the negative terminal won’t be accessible. Instead, connect the negative clamp to the engine block, alternator mount or similar bare metal.

I should acknowledge a garage debate that occasionally pops up on Internet forums: To connect the negative clamp directly to the negative battery terminal or to connect it to bare metal, such as the engine block or chassis.

You can find adherents to both methods, but securing the clamp to the battery terminal provides the least electrical resistance, thus it’s the preferred method if the negative terminal is accessible. If not, then connect it to bare metal.

Set up the car battery charger

Next, plug in the charger and select the correct setting. Consult the battery-charger owner’s manual if you’re unsure which to use. Most models have a “jumpstart,” or similar, mode designed to give the battery a potent shot of juice so you can get the engine started. They also have settings meant for long-term charging or trickle charging if you’re storing the vehicle long-term.

After selecting the right setting, plug in the charger and turn it on.

If you’re looking for a jumpstart, wait a few minutes, or the duration given in the owner’s manual. Check the indicator lights or gauge, if equipped, to determine the battery’s charge level.

Once charged, shut off the battery charger, disconnect it and start the engine.