How to Jump-Start a Car Battery
What you need to do before you turn the key
A dead battery is one of the most common reasons a car won't start. Before you attempt a jump-start, you need to know whether your battery is actually dead or whether something else is wrong. A dead battery usually means you'll hear a rapid clicking sound when you turn the key, or nothing at all — but the dashboard lights and headlights still work. If the engine turns over but won't catch, or if you smell burning, the problem is likely something else and jump-starting won't help.
Once you've confirmed the battery is dead, you'll need a second vehicle with a working battery, a set of jumper cables, and a safe location away from traffic. Never attempt a jump-start on a busy road. If you're stranded on a highway, turn on your hazard lights, stay in the car with your seatbelt on, and call for roadside assistance instead. If you're in a parking lot or residential area, you can proceed safely.
Check both batteries before you connect anything. If either battery is cracked, leaking, or visibly damaged, do not attempt a jump-start — call for help. If both batteries look intact, make sure both vehicles are turned off before you touch the cables.
Key Takeaways
- A dead battery produces a clicking sound or silence when you turn the key, but your lights and dashboard still work.
- You need jumper cables, a second vehicle with a working battery, and a safe location away from traffic.
- Always connect the positive cable to the dead battery first, then to the working battery, then the negative cable in reverse order.
- Let the working vehicle run for two to three minutes before starting the dead car, and drive for at least 20 minutes afterward to recharge the battery.
- If the car won't start after a jump-start, or if the battery is cracked or leaking, call for roadside assistance instead of trying again.
Connecting the jumper cables in the right order
The order in which you connect the cables matters. Connecting them wrong can damage both vehicles or create a spark near the battery. Always follow this sequence: positive to dead, positive to working, negative to working, negative to dead.
Start by opening both hoods and locating the batteries. The positive terminal is marked with a plus sign (+) or a red cap. The negative terminal is marked with a minus sign (−) or a black cap. Attach the red clamp of the jumper cable 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 remaining black clamp to an unpainted metal surface on the engine block of the dead car — not directly to the negative terminal. This last step grounds the connection and reduces the risk of sparks.
Once all four clamps are secure, start the working vehicle and let it run for two to three minutes. This gives the dead battery a chance to accept a charge before you try to start the disabled car.
Starting the car and removing the cables
After the working vehicle has run for a few minutes, try to start the dead car. Turn the key or press the start button as you normally would. If the engine turns over and starts, let it run for a few seconds before proceeding. If nothing happens, wait another minute and try again. Do not crank the engine repeatedly — this drains both batteries and can damage the starter.
Once the dead car is running, remove the cables in reverse order: black clamp from the dead car, black clamp from the working car, red clamp from the working car, red clamp from the dead car. Remove them slowly and carefully to avoid creating sparks. Keep both vehicles running for at least one minute after the cables are disconnected.
Drive the previously dead car for at least 20 minutes without stopping. This allows the alternator to recharge the battery. If you stop too soon, the battery may not have enough charge to start the car again.
When a jump-start won't work
Some situations require professional help instead of a jump-start. If the car won't start even after a successful jump-start, the battery may be too damaged to hold a charge, or the problem may not be the battery at all. A faulty alternator, a bad starter motor, or a fuel pump failure can all produce symptoms similar to a dead battery.
If you see corrosion (a white, blue, or green crusty buildup) on the battery terminals, you can try cleaning it off with a wire brush or baking soda and water before attempting a jump-start. Corrosion can prevent a good electrical connection. However, if the battery itself is cracked, leaking, or swollen, do not attempt a jump-start. Call for roadside assistance or a tow truck instead.
If you've tried jump-starting twice and the car still won't start, stop trying. Repeated attempts can overheat the battery and create a safety hazard. Contact a mechanic or roadside assistance service to have the battery tested or replaced.
Preventing dead batteries in the future
Most car batteries last three to five years. If your battery is older than that, have it tested at an auto parts store or mechanic — many do this for free. A battery that's losing its ability to hold a charge will eventually leave you stranded.
Common causes of dead batteries include leaving headlights or interior lights on overnight, running the radio or air conditioning while the engine is off, and extreme cold weather. In winter, a battery loses about half its power, so older batteries are more likely to fail in cold months. If you live in a cold climate or have an older vehicle, keep jumper cables in your car at all times.
If you frequently forget to turn off lights, consider a vehicle with automatic headlight shutoff. If you use your car's electrical system while parked, make sure the engine is running. These small habits can add years to your battery's life and keep you from being stranded.
What to do if you don't have jumper cables
If you're stranded without jumper cables, you have a few options. Some newer cars have a jump-start terminal under the hood that's separate from the battery — check your owner's manual to see if yours does. If it does, you can use this terminal instead, which is safer and easier than connecting directly to the battery.
If your car doesn't have a jump-start terminal and you don't have cables, call for roadside assistance. Most auto insurance policies include roadside assistance coverage, and many credit card companies offer it as a cardholder benefit. AAA and other roadside assistance services can dispatch a tow truck or a technician with jumper cables to your location. This is the safest option if you're on a busy road or uncomfortable attempting a jump-start yourself.
You can also ask other drivers in a parking lot if they have jumper cables and are willing to help. Many people carry them, and most are willing to assist. If someone offers to help, follow the same connection sequence described above.
Frequently Asked Questions
Can I jump-start a car in the rain?
It's safer to wait if possible, but if you must jump-start in light rain, keep the battery terminals dry and avoid touching metal parts with wet hands. Heavy rain or standing water creates a risk of electrical shock. If it's storming, call for roadside assistance instead.
How long should I let the working car run before starting the dead one?
Two to three minutes is usually enough for a standard battery. If the dead battery is very old or the weather is very cold, wait up to five minutes. Longer waits don't help — the dead battery won't accept more charge just from sitting connected.
What if the jumper cables get hot while I'm using them?
Hot cables usually mean there's a poor connection at one of the clamps. Stop immediately, disconnect the cables, and check that each clamp is making firm contact with the terminal. Corrosion or loose clamps are the most common cause. Clean the terminals and try again.
Can I jump-start a car with a completely dead battery, or does it need some charge?
A completely dead battery can still be jump-started. The working vehicle's battery provides the initial power. However, if the dead battery is so old that it won't hold any charge even after a successful jump-start, it needs to be replaced.
Do I need to disconnect the negative terminal before jump-starting?
No. Some older manuals recommend this, but modern vehicles don't require it. Simply connect the cables in the correct order and proceed. Disconnecting the negative terminal can erase your vehicle's computer settings and is unnecessary.