How to Jump-Start a Car Battery Safely

Jump-starting supplies temporary electrical power so a car with a discharged battery can start. It is not a repair: once running, the car may still need a battery test or charging-system inspection. Before connecting anything, check the owner’s manuals for the vehicle and the jump starter or donor car. Battery location and connection points vary, and some vehicles require designated terminals or a particular procedure.

What You’ll Need

A set of insulated jumper cables in good condition, or a compatible portable jump starter.
A donor vehicle with a compatible 12-volt system, if using cables. Follow both vehicles’ manuals; do not assume that vehicles with different battery types or electrical systems can be connected.
Safety glasses and gloves if available. Keep jewelry, loose clothing, and tools away from the battery and moving engine parts.
A well-ventilated, safe place to work. Put both vehicles in Park (or neutral for a manual transmission), apply the parking brakes, and turn off accessories and ignitions before connecting.

Step-by-Step

Check the battery and instructions. Read the manuals for the required connection points and any restrictions. Do not jump-start a battery that is frozen, swollen, cracked, leaking, unusually hot, or giving off a strong sulfur-like odor. Do not proceed if cables are damaged, terminals are loose, or the instructions prohibit a jump start. Call roadside assistance or a qualified technician instead.
Position the vehicles safely. Park close enough for the cables to reach, but do not let the vehicles touch. Set both parking brakes, select Park or neutral, and switch off both ignitions, lights, climate controls, and other accessories. Keep people clear of the engine bays and keep sparks, flames, and smoking materials away from the batteries.
Identify the terminals. Find the positive (+) and negative (−) terminals on the discharged battery, or the remote posts specified in the manual. Clean, dry connection points are best. Check the clamps for damage and make sure they cannot reach a fan, belt, or other moving part. Never guess at a terminal’s polarity.
Attach the first red clamp. Connect one red (+) cable clamp to the positive terminal or designated positive post on the discharged vehicle.
Attach the second red clamp. Connect the other red (+) clamp to the positive terminal or designated positive post on the donor vehicle. Keep the red clamps from touching each other or any metal.
Attach the first black clamp. Connect one black (−) clamp to the negative terminal on the donor battery, unless that vehicle’s manual specifies a different connection point.
Ground the final black clamp. Connect the remaining black (−) clamp to the disabled vehicle’s designated ground point: usually an unpainted, sturdy metal point on the engine or chassis, away from the battery and moving parts. Use the location given in the manual. This helps keep any connection spark away from the battery. Do not attach it to fuel lines, painted or thin metal, or an arbitrary part.
Start the donor vehicle. Start it and let it run at idle if the manual permits. Do not rev the engine to force a start. With a portable jump starter, follow its own connection and activation instructions instead; it is not used like a donor car.
Try the disabled vehicle. Wait a few minutes if the manuals recommend it, then attempt to start the disabled vehicle. Use short attempts and pause between them; repeated long cranking can overheat the starter and cables. If it does not start after a few attempts, stop and see Troubleshooting rather than continuing to crank.
Disconnect in reverse order. Once the disabled vehicle starts, remove the black clamp from its ground point, then the black clamp from the donor vehicle. Remove the red clamp from the donor, then the red clamp from the started vehicle. Keep clamps from touching one another or metal surfaces. For a jump starter, follow its specified shutdown and removal sequence.
Let the car run and arrange a check. Follow the owner’s manual about how long to run or drive the vehicle. A short drive may not fully recharge a deeply discharged battery. If the car stalls, struggles to restart, or the battery warning light stays on, get professional help rather than relying on another jump.

Common Mistakes

Reversing polarity: Connecting positive to negative can cause sparks and serious electrical damage. Match the + and − markings at both ends before attaching each clamp.
Putting the final black clamp on the dead battery: The usual safer method is a designated chassis or engine ground away from the battery. Follow the vehicle manual if it specifies another point.
Letting clamps touch: Clamps that meet while connected can short-circuit. Hold insulated handles and keep cables separated throughout the process.
Ignoring damage or freezing: A compromised battery can be dangerous to jump. Do not try to thaw it with a flame or jump it while frozen.
Cranking repeatedly or revving the donor: This can strain equipment without solving the cause. Stop after a few unsuccessful attempts and seek assistance.
Assuming a jump fixes the problem: A discharged battery may be old or faulty, or the vehicle may have a charging-system or electrical issue. A successful start does not identify the cause.

Tips

Keep jumper cables or a charged jump starter in the vehicle, and inspect cables occasionally for worn insulation, bent clamps, or corrosion.
Check the manual before using a donor vehicle on a hybrid, electric vehicle, or vehicle with a 48-volt or other nonstandard system. Some vehicles can provide a jump only from designated low-voltage terminals; high-voltage components are not jump-start points.
Do not use a hybrid or electric vehicle as a donor unless its manual explicitly permits it. Follow its specific instructions exactly.
Make sure the portable jump starter’s voltage and operating instructions match the vehicle. Connect it only at the marked posts and do not leave it attached longer than its instructions allow.
If a vehicle repeatedly needs a jump, have its battery and charging system checked. Avoid treating regular jump-starts as routine maintenance.

Troubleshooting

The engine does not turn over: Turn everything off and check that the clamps are firmly attached to the correct marked points and that the ground is secure. Check the manuals and jump-starter indicators. If connections are correct and it still will not crank after a few tries, stop; the battery may be too damaged or another fault may be present.

You hear clicking, but it will not start: The battery may be severely discharged, the terminal connections may be poor, or the starter or electrical system may have a problem. Do not keep cranking. Disconnect safely if necessary and call for roadside assistance.

The engine cranks but does not start: A jump may have restored electrical power without fixing a fuel, ignition, or other engine problem. Stop attempting repeated starts and arrange professional diagnosis.

A clamp sparks heavily, cables get hot, or you see smoke: Stop immediately. If safe, switch off the vehicles and disconnect only in accordance with the manuals; do not touch hot cables or a smoking battery. Move away and call emergency services if there is fire or immediate danger, otherwise contact roadside assistance.

The car starts but soon stalls or will not restart: The battery may not be holding a charge, or the charging system may not be working. Do not assume that extra driving will solve it; arrange a battery and charging-system check.

Frequently Asked Questions

How long should I leave the jumper cables connected?

Follow the manuals for the vehicles and cables; some recommend a short wait with the donor idling before attempting a start. Do not leave cables connected indefinitely or keep trying to start the vehicle repeatedly.

Can I jump-start a car in the rain?

Light rain does not automatically make a jump unsafe, but avoid standing water and do not handle damaged cables or exposed electrical parts. If conditions make it hard to work safely, wait or call for help.

Can I jump-start a car with a portable jump starter?

Yes, if it is rated for the vehicle and its instructions permit use. Connect to the marked terminals in the prescribed order, and follow the unit’s activation and removal directions.

How long should I drive after a jump-start?

There is no single reliable time that fully recharges every battery. Follow the manual, and arrange a proper battery charge or test if the battery was deeply discharged or the vehicle has trouble restarting.

What if the battery terminals are corroded?

Do not force clamps onto loose, badly corroded, or damaged connections. Avoid touching residue, and have the connections cleaned and inspected safely before attempting a jump.

Can I jump-start a car with a dead battery more than once?

A repeat jump may work, but recurring discharge means the cause needs attention. Have the battery, charging system, and possible electrical drain checked rather than relying on repeated starts.

Further reading: NHTSA. Details can change, so check the official page for anything that matters to you. Spotted a mistake? Tell us. How we write an answer.