How to charge a dead car battery with jumper cables

A dead battery is no-one's idea of fun, but you can still jump a car by connecting the bad battery to a fully charged one using jumper cables.

Here, we show you how to jump start a car, assuming that the charged battery is in another vehicle.

Bear in mind that depending on how dead the car battery is, jumper connections may or may not start a vehicle immediately. After you've connected the two, you may need to start the car with the healthy battery, and spend a few minutes with the two hooked up to give the dead battery some charge. 

It’s also a good idea to read your car’s manual carefully to see if there are any special recommendations to be observed when jump starting. And if you're in any doubt, call AAA or your local roadside assistance, who will have the equipment to get your car running without any risk of damage.

Your Step-by-Step Guide To Jumping A Car

Precautions:

• Position the vehicles close enough so that the jumper cables will reach easily, but MAKE SURE THE VEHICLES DON’T TOUCH EACH OTHER!
• Make sure the cables will not be damaged by the fan, drive belts or any other moving parts when the vehicles are started.
• Make sure the booster battery is the same voltage as the dead one in the vehicle. Nearly all modern car and truck batteries are 12 volts.
• Make sure the ignition switches of both cars are in the off position, and the transmissions are in Neutral (manual) with the parking brake set, or Park (Automatic).
• Turn off the lights and other electrical loads on the car with the dead battery, although if it is a modern car with a computer, it’s a good idea to turn on the heater blower motor which will minimize the damage an excessive electrical surge can cause.
• It’s a good idea to wear safety goggles, because there is always a chance of an explosion and batteries are full of acid.

Make the jumper cable connections in EXACTLY this order:

1. Connect the red jumper cable to the positive terminal of the dead battery (or jump start terminal on a car with a remote-mounted battery).
    
2. Connect the opposite end to the positive terminal of the booster battery or jump start terminal.
    
3. Connect the black jumper cable to the negative terminal of the booster battery or jump start terminal.
    
4. Connect the other end of the black cable to a well-grounded bolt or bracket on the engine block of the vehicle being jumped, not the battery itself. This prevents sparks near the battery which may cause an explosion.
    
5. Start the engine of the vehicle with the good battery and let it run at a moderate speed to charge both batteries.
    
6. Start the engine of the vehicle with the discharged battery.
    
7. Reduce the engine speed to idle on both vehicles and leave all switches off to prevent damage to the vehicle electrical system.
    
8. Remove the jumper cables in the reverse order they were attached, making sure to never touch the red and black terminals to each other.

If the charging system and the battery of the car which had to be jumped is in good condition, 30 minutes of driving should being it back up to a full charge.

Remember, sometimes in extreme cold conditions a perfectly functional car may need a boost to get started because batteries put out less energy the lower the temperature, while at the same time need more power to turn in the cold.

Many Americans are driving less due to the pandemic, often leaving their car parked for days or even weeks. As a car sits, the battery drains. This is especially true for relatively new vehicles with various electronic systems that consume energy even when the car is parked. Consequently, many motorists have needed a jump-start recently.

In fact, AAA has seen a 10 percent rise in jump-start service calls this past year, with a striking 56 percent increase for jump-starts at residences.

Jump-starting a car used to be a simple affair, but since cars have become more complex there are new risks, and you should be cautious if you jump-start on your own. Plus, you might want to think twice about asking a stranger for help.

More on Cars & Cold Weather

“When a vehicle battery dies, the most common solution is to jump-start the battery using jumper cables and another vehicle. However, if proper steps are not taken, there is no guarantee this method won’t cause damage to the vehicle,” says David Bennett, AAA’s manager for repair systems. “For example, attempting to jump-start a damaged or frozen battery could cause significant damage to the vehicle and worse, individuals around the vehicle.”

John Banta, Consumer Reports’ lead battery tester, warns that you could fry a key electronic component by not following the proper procedures, and there are the time-old concerns about sparks and battery acid. It's best to ask a professional for help.

“Due to the complexity of the electrical system in vehicles, appropriate tools and procedures are crucial to prevent hundreds—if not thousands—of dollars in repairs,” says Ricky Hendan, senior tech training and research analyst at AAA.

AAA service technicians are trained on battery technology and vehicle types. Plus they can access an online database for the appropriate procedure based on the make, model, and engine. In cases where they can’t start the old battery, some carry replacements with them.

But some cars will need a trip to a dealer for a battery replacement because they require special computer resetting, says David Trezza, senior test project leader at Consumer Reports. If AAA can't put a battery in, it can tow you to the dealer.

If you must jump-start your vehicle on your own, Consumer Reports' chief mechanic, John Ibbotson, recommends following the owner's manual to the letter. “These manuals spell out step-by-step instructions on the proper way to jump-start the car," he says. "If in doubt, seek help.”

Remember that jumper cables usually have a set of clamps, one marked red for positive and the other black for negative. And battery terminals are usually marked with a + for the positive terminal and a - for negative. You might need to wipe off some grime to see them if your battery is dirty.

• Park the car you’ll use for jump-starting next to the one with the dead battery, positioned close enough so that the cables will reach. The vehicles shouldn't touch one another.
• Turn off the ignition on both cars.
• First, clamp one end of the positive cable to the dead battery’s positive clamp.
• Now have a helper connect the other end of that cable to the other battery’s positive clamp.
• Next, connect the negative cable to the negative terminal on the good battery.
• Finally, connect the other end of the negative cable to a ground on the vehicle with the dead battery. This can be the engine block or another metal surface away from the battery. Be careful not to touch the two ends of the cable together while doing this.
• Start the rescue car that is providing the electricity.
• Start the car with the weak battery. If it doesn’t start, check your connections and tighten or clean as needed.
• If it does start, let the problem car run for at least 20 minutes to allow the battery to recharge before shutting it off.
• If it still doesn’t start, there may be another problem. Call a local service station for help.
• Disconnect the cables in the reverse order.

Cars need to be driven regularly to allow the alternator to maintain the battery’s charge level. If you need to park your car for an extended period, consider using a trickle charger or battery maintainer. These devices can replenish a drained battery. The better models can replenish the battery and potentially extend its service life.

Car batteries typically last three to five years, according to AAA, depending on use and temperatures. Hot weather is far worse on battery life than cold weather.

“Routine inspection is as important for the battery as it is for the rest of the car,” says CR’s Banta.

To avoid being stranded, you should be diligent about servicing and replacing your car’s battery, Banta says. He recommends having the battery load tested annually after it’s 2 years old if you live in a warmer climate and 4 if you live in a colder climate. Doing so tests its ability to hold voltage while being used, and the results will let you know when it’s time to start shopping for a replacement.

It's better to careful about maintaining and replacing your battery than stretching every last start from it and risking being stranded.

Some auto parts stores, like AutoZone, will test your battery free of charge and install a replacement if needed.

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