A dead battery in your car can mean the difference between getting home safely and being stuck somewhere for hours. Here's a step-by-step guide on how to revive your car and get you back on the move, with tips from an expert mechanic.
Road & Track spoke with Kevin Hines, senior technician at McLaren Philadelphia, to learn the correct way to revive a dead battery and jump-start a car safely. Hines is North America's only factory-certified McLaren F1 technician, which means his day job revolves around working on $20 million exotics. If anyone understands how to bring an electrically-starved car back from the dead, it's him.
Before you read any further, we suggest consulting your car's owner's manual for exact instructions on how to jump-start your vehicle. Your manufacturer's suggestions may differ from the instructions below.
"My first choice would be to use a battery charger if you were in a situation with a dead battery," Hines tells Road & Track. Charger boxes and trickle chargers, most often found in mechanic shops and storage facilities, are used to keep projects or stored vehicles charged as they sit for long periods of time. Their uses are limited, as Hines points out. Not everyone has the luxury of discovering they have a dead battery while their car is nestled somewhere safe and away from the elements.
Hines's second choice? "I always carry a jumper pack," he tells us. "They're tiny, and they're $100 or less. They work, they're really incredible. It's like a tiny little box of magic."
Having a jumper pack tucked inside your glove box or trunk can save you a world of headache, and might even save someone else some trouble. "I've been the hero several times because I always have one," Hines says. "People always appreciate when a hero shows up."
If you do plan to keep a jumper pack onboard, you should obviously make sure that it's charged at all times. A dead jumper pack won't do you any good in an emergency situation. Here's one we love:
How to Jump Start a Car with Cables
So you've found yourself in a situation where the only way to get a car's battery revived is through a set of jumper cables. Here's how it's done.
Before you get to connecting the two cars together, inspect the batteries to ensure there are no signs of damage. If terminals look physically damaged, or there's a buildup of battery acid around them, those are good signs you need a new battery. If possible, replace the dead battery instead of trying to jump it. If you're in a situation where the battery must be jumped, take an abundance of precaution connecting it to the other car.
If a battery is swollen beyond its normal dimensions, you could have an even bigger problem on your hands, according to Hines. Most car batteries contain a liquid that's part sulfuric acid and part water. Over time, the acid's potency can weaken to the point where the liquid is mostly just water. That means it can freeze and expand if it's left out in the cold. "If you suspect at all the dead battery is frozen, do not try to jump start it," he tells us. "There's a possibility that it could explode. And an explosion with battery acid is not a party you want to get into."
It's also a good idea to inspect the cables themselves for signs of damage or exposed wire. You want to ensure they'll be able to make a good connection between the two car batteries without grounding out on another part of the car.
The next step? After you get the cars parked close enough where a connection can be made, make sure both cars are completely, totally shut off. Yes, that means the car with the dead battery as well. "If [the dead car's] ignition is on, then you have more of a load than just a dead battery," Hines says. "So when you make the connection [to the good car] you will have sparks, and sparks are scary."
Cable Connection Order
Once the cars are in the right place and turned all the way off, you can start connecting the cables. First, take one lead of the positive cable (usually marked in red or orange) and connect it to the positive terminal (+) of the dead battery. Next, take the other side of that same positive cable and connect it to the positive terminal (+) of the good battery. Now, take one lead of the negative jumper cable (almost always marked in black) and connect it to the negative terminal (-) on the good battery. "The last remaining negative jump lead would go to, preferably, a ground point on the dead car," Hines says. "If that can't be found then it goes straight to the negative battery terminal. (-)"
Make sure all four leads have good, solid connections to their jump points. You don't want any of them popping off if you bump into the wires or either of the cars. After that's done, start the car with the good battery. Let it run for 15 to 20 minutes. "The alternator of the good car will charge up the flat battery," Hines says. After that, you can go ahead and attempt to start the car with the dead battery. If you've done everything right (and the dead car is in good health), it should start right up.
Once the dead car is running, hop out and disconnect the cables in the opposite order you connected them. You don't have to rush this part, according to Hines. Having both cars running with the batteries connected won't do any immediate harm. "People think of the battery as something that only puts out or stores electricity," he tells us. "But it can also act as a sort of electrical shock absorber. So when you're jump-starting a car, the battery will do its job and absorb that spike."
Of course, that doesn't mean you should leave the two cars attached for long. "I'd disconnect [the wires] as soon as you get it started," Hines tells us.
What If the Car Dies after You Remove the Cables?
If your car fails to stay running after you disconnect the wires, you likely have a problem with the charging system, says Hines. Your alternator could be going bad, or there could be damage to one of your engine's accessory belts or pulleys. Inspect the engine bay for any damage, and consult a professional if you can't remedy the problem.
How Can I Tell If My Battery Is Going Bad?
Most car batteries aren't designed to last more than four or five years. Good news is, your car will show signs of a failing battery before it clonks out for good. If your car is sluggish to start, doesn't start after a limited amount of time sitting, or has pulsating dash lights, your battery is likely on its way out. Consult a professional to find out for sure.