How To Jump-Start A Car

How to Jump Start a Car
Cars and batteries may look newer nowadays, but jump starting hasn’t changed since the early days of motoring. The process isn’t hard, but it is important to get the steps right and put safety first. Getty Images

From time to time, every driver turns the key or presses “START” to find … nothing. A jump-start is the most common way to get back on the road, even if it’s just the road to the nearest place that sells replacement batteries. But a few things can go wrong with serious consequences, so knowing how to jump start a car safely is key. There are two basic scenarios to this in 2021, either keeping a portable battery charger with you in the car or the traditional jump-start scenario involving another car and a set of jumper cables. 

Flying Solo With A Portable Battery Charger 

If the car that won’t start is nosed in up against a wall, parked in a lot full of cars owned by total strangers, or out in the middle of nowhere, one of the greatest things to have in the trunk is a portable vehicle jump-starter. Usually the size of a small backpack, they’re battery-powered with cords and clamps attached.   

Read and follow the instructions carefully and remember to recharge it after. It’s also a good idea to check the state of charge of a portable jump-starter on a regular basis to make sure it will work the next time you need it. 

There’s also a new breed of battery-free packs that use solid-state capacitors and an external power source.  The advantage is that these can be much smaller, fitting in a glove box or console instead of a trunk. Again, read and follow the instructions carefully. 

Good Battery Settings
Pardon the dirty batteries. To illustrate how to attach cables, we did a real jump using two of Forbes Wheels’ own vehicles in real-world conditions. The car providing the charge should have the red (positive) cable attached to the positive terminal, which may be under a removable cover (as might the entire battery). The black (negative) cable of the charging vehicle should be attached after the positive cables are attached, but should be clamped to the negative terminal of the charging battery. Forbes Wheels

The Classic Jump-Start Scenario 

For this, you need a set of jumper cables and another vehicle with a good battery. It’s also best to use the buddy system and have a friend helping you. 

The first thing is to open the hoods of both the vehicle that needs the jump-start and the one that’s going to provide the power. Check to see exactly where the battery is in both vehicles.  

There’s no standard requirement for where a battery is located on a vehicle and while most batteries can be found under the hood, some vehicles may have the battery in the trunk or even under the back seat through an access panel. Where the two batteries are and how long the jumper cables are is going to determine where the car with the good battery has to park to make this work. 

Bad Battery Settings
The red (positive) cable should be attached to the positive terminal of the dead battery after the positive cable is hooked to the charging battery. The black (negative) cable should be hooked to a bare metal surface on the body, which is why that clamp is out of view here. Forbes Wheels

The Basics 

Once the vehicles are in position (but not touching each other), turn off the engine on the vehicle with the good battery. Then turn off every power-using accessory on the vehicle needing the jump start—headlights, interior light, audio system, air conditioning.   

Find the positive terminal on each battery. It’ll have a “plus” (+) sign near the terminal on the battery case or a red terminal cover.   

With the ignitions off on both vehicles, connect one end of the red jumper cable to the positive terminal of the dead battery first, and then the other end to the positive terminal of the good battery. 

Find a piece of unpainted metal in the engine compartment of the car needing the jump-start and attach one end of the other cable (some are black, some are blue) to that. Then do the same with the other end on the car with the good battery.  This provides a ground, essential for safety.   

Bad Battery Ground Cable
In this case, the black (negative) cable for the car with the dead battery is hooked to these bare metal bolts. If you can’t find any such place on your vehicle, the owner’s manual will have a recommendation. Forbes Wheels

Finding a spot of unpainted metal under the hood can be a challenge on some cars, but your owners’ manual will tell you where you’re supposed to hook the negative cable. In some cases, it may recommend the engine block.  

Touch only the insulated grips of the clamps—you’re dealing with potentially deadly voltage from the good battery.    

Drivers Start Your Engines, One At A Time 

Start the engine of the car with the good battery and let it run for a few minutes before attempting to start the other. Every minute that you do this, you’re pouring cranking amps back into the dead battery and improving your chances of getting it to turn the engine over.   

If it cranks but doesn’t turn over, wait a while longer and try again. You may want to wait 15 or so minutes. If you’ve waited more than 20 minutes and all the connections are correct, it’s very likely your battery is dead and that a jump-start isn’t possible. Only a new battery will get you moving again. 

Ready to Jump
The full setup. It’s important to keep any slack cables out of the engine bay, where they might catch on moving parts. Four minutes later, the dead car, a Mercury Grand Marquis, was up and running. Forbes Wheels

Safety First And Last 

Once the car that needs the jump-start is running, removing the jumper cables safely is every bit as important as putting them on. Carefully remove the black or blue (ground) cables first.  Make sure that they don’t touch any other metal on the way off or while you’re in the process.  The only thing touching those alligator clamps should be air. 

Especially important—don’t let the negative and positive cables touch during the removal process.  Sparks, shock and even fire can happen.   

When they’re off safely, put them away, close both hoods, but don’t shut off the engine of the car that was just jump-started. It’s going to need some time for the alternator to fully recharge the battery. The best thing is to immediately go for a drive. Go 20 minutes or more before you turn off the ignition and do that someplace where you could easily jump-start the car again if necessary. 

If you find yourself with a dead battery and none of the above jump-start scenarios are possible for whatever reason, Auto Clubs like AAA offer Emergency Roadside Service. These can be lifesavers (figuratively and literally) and memberships can pay for themselves in one well-timed rescue.