It's an essential skill that any driver should have, but if you ask five people how to jump-start a car with a run-down battery, you could get five different answers. Here's the right way to give a dead battery a boost.
Before you get started, clearly there are a few things you'll need. You'll want a pair of jumper cables, which we suggest you always keep in the trunk or stashed away in your car, and you'll need a car with a good, working battery.
Before you even get started, make sure that your jumper cables are in good condition. They should be long enough to easily reach between the car with the good battery and the car that needs juice. There should be no exposed wire, and the rubber coating should be free of cracks or damage. The clamps of the jumper cables should be clean, as should the terminals of the batteries you're connecting them to. We suggest keeping a battery terminal brush in the trunk with your jumper cables, just in case.
Once your vehicles are in place, turn both vehicles off, put them in park (or neutral for a manual) and set their parking brakes. Go ahead and pop the hoods of both vehicles and get your jumper cables ready. Photo by Michael Pedersen.
Connect the Vehicles
Remember, the red connector is positive, and the black connector is negative. The red clamp on one end connects through to the red clamp on the other; the cables don't cross in the centre.
Take care when connecting the two vehicles – when connecting one clamp, try not to let the other clamp dangle into the engine compartment or rattle around under the hood. Now then, AAA, Edmunds, and Car and Driver Magazine all agree on this order of operations:
- Firmly connect one red clamp to the positive (+) terminal on the car with the dead battery.
- Connect the other red clamp to the positive (+) terminal on the car with the good battery.
- Connect one black clamp to the negative (-) terminal on the car with the good battery.
- Connect the other black clamp to an unpainted metal surface anywhere in the engine compartment of the car with the dead battery. This will ground the connection – even a bolt or crossbar will do.
Make sure all of the connections are firm, and the clamps are tightly secured. Make sure your ground connector isn't close to any moving parts. You don't want the clamps rattling around or moving when you go to start one of the vehicles.
Start Your Engines
Start the booster car (the one with the good battery.) Starting the vehicles in this order will immediately start charging the car with the dead battery, so in most cases you don't need to let the booster car run with the dead car shut off. However, if the battery in the dead car has been dead for a long time, you may need to let the booster car idle a bit to get some charge into the dead car's battery.
Once the booster car is running, go ahead and start the dead car. It will likely start up right away, but if it doesn't, stop trying, wait a few minutes, and then try again. If it still doesn't start after two more three tries, stop trying — you don't want to damage the starter. It's possible that the battery simply won't hold a charge, or there's something else wrong with the vehicle. Photo by Doug Waldron.
Disconnect the Vehicles
If your dead vehicle does come back to life, leave it running and then slowly disconnect the cables in the reverse order as you connected them. This means disconnect the ground on the dead car first, and then the negative terminal on the good battery. Then disconnect the positive terminal on the good battery, and finally the positive terminal on the now jump-started car.
Be very careful when doing this – you're dealing with live cables. Only touch the protected clamp handles, and when you disconnect one end, don't let it dangle into the engine or allow a positive and a negative clamp to touch each other. Photo by Andy Armstrong.
With luck, you can bid your friend with the good battery farewell and drive your now jump-started vehicle to a safe location. You may need to jump-start the vehicle again the next time you turn it off, but a good 15 minutes of drive or idle time should be enough to get a good charge on your battery.
However, it's important to note that if the battery is in really bad shape, you should get to a mechanic or an auto parts store with a certified battery charger and leave your battery connected for several hours. Your alternator will definitely charge the battery while you drive, but it's not meant to provide a full charge.
Jump-Starters and Battery Kits
If you don't want to go through the hassle of finding someone to help you jump-start your car, or have to deal with roadside assistance, a jump-start kit may be a wise investment. Most are small enough to be carried in one hand and can slide into a corner of your trunk until they're needed.
When your battery dies, just pull out the jump-start kit, and depending on the model you have, connect it directly to your vehicle's battery or to a power outlet inside the car, and allow the battery to charge for 15 minutes or so before starting the vehicle. Many jump-starters will also show you the battery's overall health, and will tell you when to start the car.
Jump-starters come in different shapes and sizes, ranging from 300 amps to 3000 amps, but most fall between 400-600, which is enough for most vehicles. Just be sure to keep the jump-starter itself charged periodically, or else you'll find yourself with a dead battery and a dead jump-starter.
If you do go this route, it can save you the headache of finding a good Samaritan to help with your dead battery, but make sure to follow the instructions for a good, safe jump-start.
This story has been updated since its original publication.