The basic steps for jumpstarting a car
To jumpstart a car, you connect jumper cables from a working battery to a dead one, start the working car, wait a few minutes, then start the dead car. The working car stays running for several minutes after the dead car starts, which lets the alternator in the dead car begin recharging its battery. You then disconnect the cables in reverse order — negative from the dead car first, then negative from the working car, then positive from the working car, then positive from the dead car.
The reason for this order matters: disconnecting negative first prevents sparks that could ignite battery gases. A car with a dead battery will usually start within seconds once the cables are connected and the working car has run for a minute or two, though some batteries need three to five minutes of charging before they have enough power.
Key Takeaways
- You need jumper cables, a second car with a working battery, and both cars parked close enough that the cables reach between them.
- The working car must be running before you try to start the dead car, and should keep running for at least three to five minutes after the dead car starts.
- Connect positive cables first (red clamps to the positive terminals), then negative (black clamps to the negative terminals), then reverse the order when disconnecting.
- If the car does not start after five minutes of the working car running, the battery may be too damaged to jumpstart, and you should call a tow truck instead.
What you need before you start
You need a set of jumper cables, a second vehicle with a working battery, and enough space to park both cars close together — usually within three to four feet. Jumper cables come in different gauges (thicknesses); thicker cables work better, but any cable rated for your car's engine size will work. Most auto parts stores sell them for $15 to $40.
Both cars should be turned off before you connect anything. If either car is running when you attach the cables, you risk damaging the electrical systems in both vehicles. Check that both batteries are accessible — some newer cars have batteries under the rear seat or in the trunk, which makes jumpstarting harder but not impossible.
Connecting the cables in the right order
Position both cars so the batteries are as close as possible without the cars touching. Open both hoods and locate the battery terminals — they are usually two posts on top of the battery, one marked with a plus sign (positive) and one with a minus sign (negative). The positive terminal is usually larger and often has a red plastic cover; the negative terminal is usually smaller and has a black cover.
Attach the red clamp to the positive terminal of the dead battery first. Then attach the other red clamp to the positive terminal of the working battery. Next, attach the black clamp to the negative terminal of the working battery. Finally, attach the last black clamp to an unpainted metal surface on the dead car's engine — a bolt, bracket, or bare metal part — rather than directly to the negative terminal of the dead battery. This last step reduces the risk of sparks near the battery.
Do not let the metal clamps touch each other or touch both terminals on the same battery at the same time, as this creates a short circuit.
Starting the cars in the correct sequence
Start the working car and let it run for one to three minutes before attempting to start the dead car. This gives the dead battery time to accept a charge. Then try to start the dead car. It should turn over within a few seconds; if it does not start after five attempts, wait another two minutes and try again.
If the car still will not start after ten minutes of the working car running, the battery is likely too damaged to jumpstart. In this case, disconnect the cables and call a tow truck. Continuing to try will not help and may damage the starter motor.
Disconnecting the cables safely
Once the dead car has started, keep both cars running for at least three to five minutes. This allows the alternator in the previously dead car to begin recharging the battery. Then turn off the working car and disconnect the cables in this exact order: black clamp from the dead car first, then black clamp from the working car, then red clamp from the working car, then red clamp from the dead car.
Disconnecting in this order prevents sparks and protects both electrical systems. After you remove all cables, close both hoods and drive the previously dead car for at least twenty minutes to give the battery more time to recharge. If the car dies again within a few hours, the battery likely needs replacement.
What to do if the jumpstart does not work
If the car does not start after the working car has run for ten minutes, or if it starts but dies when ready after you disconnect the cables, the battery is probably too weak or damaged to hold a charge. A battery that is more than three to five years old is more likely to fail completely rather than just need a boost.
Other reasons a jumpstart might fail include corroded battery terminals (which you can clean with a wire brush and baking soda mixed with water), loose cable connections, or a problem with the starter motor or alternator rather than the battery itself. If you see corrosion — a white, blue, or green crusty buildup on the terminals — clean it before trying again. If the car still will not start, you will need a mechanic or tow service to diagnose the real problem.
Preventing a dead battery in the future
A battery usually lasts three to five years. If your car is older than that and the battery has never been replaced, have it tested at an auto parts store — most do this for free. A weak battery will show warning signs: the car takes longer to start, the headlights dim when you use the air conditioning, or the interior lights flicker.
Leaving lights on, running the radio with the engine off, or letting the car sit unused for weeks without driving can all drain a battery. If you know you will not drive for more than a month, disconnect the negative terminal of the battery to prevent slow drain. If you drive regularly, the alternator will keep the battery charged as long as the battery itself is in good condition.
Frequently Asked Questions
Can I jumpstart a car if the battery is cracked or leaking?
No. A cracked or leaking battery can release hydrogen gas, which is flammable. If you see cracks, white powder, or liquid around the battery, do not attempt a jumpstart. Call a tow truck and have the battery replaced before driving the car.
How long should I let the working car run before starting the dead car?
One to three minutes is usually enough. If the dead car does not start after that, wait another two to three minutes. Running the working car longer than ten minutes without starting the dead car will not help and wastes fuel.
What if I do not have jumper cables?
You cannot jumpstart without cables. Some cars come with a cable set in the trunk; if yours does not, you will need to call a tow truck or roadside information service. Stores like AutoZone and Advance Auto Parts sell cables, but you would need to get to a store first.
Is it safe to jumpstart a car in the rain?
Yes, as long as water is not pooling directly on the battery terminals. Wipe the terminals dry before connecting cables. The risk of electrical shock from a car battery is very low because the voltage is only 12 volts, even though the current is high.
Can I jumpstart a car with a different type of battery?
Yes. A standard lead-acid battery can jumpstart another lead-acid battery regardless of the brand or exact model, as long as both are 12-volt batteries. Most cars use 12-volt batteries. Hybrid and electric cars may have different battery systems — check your owner's manual before attempting a jumpstart.