How to Jump Start a Car
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A dead battery strands more drivers than any other fault, but a jump start takes ten minutes with a set of cables and a second vehicle — or a portable jump starter. The cable order matters: connecting in the wrong order can spark near the battery or damage electronics. Follow the steps in order.
Car batteries can release hydrogen gas, and a spark at the wrong moment can cause burns. Never jump a battery that is cracked, leaking, swollen, or frozen. If the battery shows any of those signs, replace it instead. Keep cable clamps from touching each other once connected to a battery.
What you'll need
- Jumper cables (thick gauge, 4–6 gauge is best) or a portable jump starter
- A second vehicle with a healthy battery (if using cables)
- Gloves and eye protection (recommended)
The steps
Tap through one step at a time — built for one-handed use at the roadside — or switch to all 11 steps to read ahead or print.
Step 1 of 11: Park the donor car close
Step 1: Park the donor car close
Bring the working vehicle nose-to-nose (or side-by-side) with the dead car so the cables reach both batteries — typically within 2 feet. The vehicles must NOT touch each other. Switch off both engines, set both parking brakes, and remove the keys.
Two touching vehicles can create a ground path — keep a gap between the bodywork.
Step 2: Turn everything electrical off
On the dead car, switch off the headlights, interior lights, radio, A/C, and unplug phone chargers. This protects sensitive electronics from a voltage surge when the battery comes back to life.
Step 3: Identify the terminals
Find the positive (+, red cover, marked POS) and negative (−, black, marked NEG) terminals on both batteries. Some cars hide the battery in the trunk or under a seat but provide marked jump-start posts under the hood — check your owner's manual. Brush away heavy corrosion only with eye protection on.
Step 4: Red clamp to the dead battery's positive (+)
Attach one red clamp firmly to the positive (+) terminal of the DEAD battery first. Wiggle it so the teeth bite into clean metal.
Step 5: Red clamp to the donor battery's positive (+)
Attach the other red clamp to the positive (+) terminal of the DONOR battery. Once both red clamps are on, never let the loose black clamps touch them.
Step 6: Black clamp to the donor battery's negative (−)
Attach one black clamp to the negative (−) terminal of the DONOR battery.
Step 7: Black clamp to bare metal on the dead car — NOT the battery
Attach the final black clamp to an unpainted metal surface on the dead car, away from the battery: a clean engine bracket, bolt, or chassis point works. This completes the circuit away from the battery so any spark cannot ignite hydrogen gas the battery may vent.
Do not clamp to the dead battery's negative terminal — that is the single most common jump-start mistake, and it risks a battery explosion.
Step 8: Start the donor car, then wait
Start the donor vehicle and let it run at a gentle fast idle (or just idle) for 2–5 minutes. This pushes charge into the dead battery through the cables.
Never run either engine in a closed garage. Exhaust carbon monoxide is colorless and odorless, and it builds to dangerous levels in an enclosed space long before you feel anything wrong. Open the door fully and push the car out, or work in the open air.
Step 9: Start the dead car
Try starting the dead car. If it cranks weakly or not at all, wait another 2–5 minutes with the donor running and try again. If it still will not start after a few attempts, the battery may be too far gone or another fault is at play — stop cranking to avoid overheating the starter.
Step 10: Disconnect in exact reverse order
Remove the clamps in the reverse order you attached them: 1) black from the grounded metal, 2) black from the donor negative, 3) red from the donor positive, 4) red from the formerly-dead battery. Do not let clamps dangle and touch each other or the car body while any end is still connected.
Step 11: Keep the engine running — then get the battery tested
Drive (do not just idle) for at least 15–30 minutes to let the alternator recharge the battery. Then have the battery and charging system tested — most parts stores do it free. If the battery is over 3–5 years old or drained for no obvious reason, plan on a replacement.
If the car dies again at the next stop, the alternator may not be charging — do not keep jump-starting; have the charging system tested.